Microcirculation in insulin resistance and diabetes: more than just a complication

The Metabolic Syndrome, a Human Disease

This review focuses on the question of metabolic syndrome (MS) being a complex, but essentially monophyletic, galaxy of associated diseases/disorders, or just a syndrome of related but rather independent pathologies. The human nature of MS (its exceptionality in Nature and its close interdependence with human action and evolution) is presented and discussed. The text also describes the close interdependence of its components, with special emphasis on the description of their interrelations (including their syndromic development and recruitment), as well as their consequences upon energy handling and partition. The main theories on MS's origin and development are presented in relation to hepatic steatosis, type 2 diabetes, and obesity, but encompass most of the MS components described so far. The differential effects of sex and its biological consequences are considered under the light of human social needs and evolution, which are also directly related to MS epidemiology, severity, and relations with senescence. The triggering and maintenance factors of MS are discussed, with especial emphasis on inflammation, a complex process affecting different levels of organization and which is a critical element for MS development. Inflammation is also related to the operation of connective tissue (including the adipose organ) and the widely studied and acknowledged influence of diet. The role of diet composition, including the transcendence of the anaplerotic maintenance of the Krebs cycle from dietary amino acid supply (and its timing), is developed in the context of testosterone and β-estradiol control of the insulin-glycaemia hepatic core system of carbohydrate-triacylglycerol energy handling. The high probability of MS acting as a unique complex biological control system (essentially monophyletic) is presented, together with additional perspectives/considerations on the treatment of this 'very' human disease.

Protection by metformin against severe Covid-19: an in-depth mechanistic analysis

Since the outbreak of Covid-19, several observational studies on diabetes and Covid-19 have reported a favourable association between metformin and Covid-19-related outcomes in patients with type 2 diabetes mellitus (T2DM). This is not surprising since metformin affects many of the pathophysiological mechanisms implicated in SARS-CoV-2 immune response, systemic spread and sequelae. A comparison of the multifactorial pathophysiological mechanisms of Covid-19 progression with metformin's well-known pleiotropic properties suggests that the treatment of patients with this drug might be particularly beneficial. Indeed, metformin could alleviate the cytokine storm, diminish virus entry into cells, protect against microvascular damage as well as prevent secondary fibrosis. Although our in-depth analysis covers many potential metformin mechanisms of action, we want to highlight more particularly its unique microcirculatory protective effects since worsening of Covid-19 disease clearly appears as largely due to severe defects in the structure and functioning of microvessels. Overall, these observations confirm that metformin is a unique, pleiotropic drug that targets many of Covid-19′s pathophysiology processes in a diabetes-independent manner.

Metformin prevents endothelial oxidative stress and microvascular insulin resistance during obesity development in male rats

Insulin increases muscle microvascular perfusion, which contributes to its metabolic action in muscle, but this action is impaired in obesity. Metformin improves endothelial function beyond its glucose lowering effects. We aim to examine whether metformin could prevent microvascular insulin resistance and endothelial dysfunction during the development of obesity. Adult male rats were fed a high-fat diet (HFD) with or without simultaneous metformin administration for either 2 or 4 wk. Insulin's metabolic and microvascular actions were determined using a combined euglycemic-hyperinsulinemic clamp and contrast-enhanced ultrasound approach. Compared with chow-fed controls, HFD feeding increased body adiposity without excess body weight gain, and this was associated with a marked decrease in insulin-mediated whole body glucose disposal and abolishment of insulin-induced muscle microvascular recruitment. Simultaneous administration of metformin fully rescued insulin-induced muscle microvascular recruitment as early as 2 wk and normalized insulin-mediated whole body glucose disposal at week 4. The divergent responses between insulin's microvascular and metabolic actions seen at week 2 were accompanied with reduced endothelial oxidative stress and vascular inflammation, and improved endothelial function and vascular insulin signaling in metformin-treated rats. In conclusions, metformin could prevent the development of microvascular insulin resistance and endothelial dysfunction by alleviating endothelial oxidative stress and vascular inflammation during obesity development.NEW & NOTEWORTHY Muscle microvascular insulin action contributes to insulin-mediated glucose use. Microvascular insulin resistance is an early event in diet-induced obesity and is associated with vascular inflammation. Metformin effectively reduces endothelial oxidative stress, improves endothelial function, and prevents microvascular insulin resistance during obesity development. These may contribute to metformin's salutary diabetes prevention and cardiovascular protective actions.

Microcirculatory Responses to Muscle and Tendon Exercises in Individuals With and Without Type 2 Diabetes Mellitus and the Association Between Microcirculatory and Exercise Performance

Background: This study aimed to measure and compare (1) the microcirculation and microcirculatory responses of the muscles and tendons at rest and during isometric muscle contractions in participants with and without diabetes mellitus (DM) and (2) to determine correlations between microcirculation and muscle strength. Methods: Sixty-three participants with type 2 DM and 42 physically matched controls were recruited. Baseline measurements of the microcirculation of the rectus femoris (RF) and medial gastrocnemius (MG) muscles and patellar (PT) and Achilles tendons (AT), as well as their microcirculatory changes during maximal isometric exercises, were performed and recorded by using near-infrared spectroscopy and a red laser. Data on various laboratory tests (including glycated hemoglobin, triglyceride, high-density cholesterol), the monofilament test, and the ankle-brachial index were also obtained. Results: The baseline measurements indicated that, compared with the controls, the diabetic participants had lower oxygen saturation (SpO₂) in their RF and MG muscles (both P < 0.001), and the total hemoglobin in the diabetic PT and AT was higher (P = 0.001 and P = 0.01). The minimal SpO₂ levels in the aforementioned muscles during isometric contractions were lower in the diabetes group than in the control group (P ≤ 0.001). Furthermore, there were correlations between the microcirculatory change of the RF muscle and the knee extension force. Conclusions: This study demonstrated the effects of diabetes on the microcirculation of skeletal muscles and tendons during baseline measurements and responses to maximal isometric exercises. The results support the need for preventive strategies for diabetic muscles to prevent adverse complications when performing resistance training.

The safety and efficacy of PDE5-inhibitors-vardenafil on treating diabetes mellitus erectile dysfunction: A protocol for systematic review and meta analysis

BACKGROUND

Diabetic mellitus erectile dysfunction (DMED) refers to erectile dysfunction (ED) secondary to diabetes. As people's lifestyle changes and the population ages, the incidence of DMED continues to increase. Many clinical trials have proven that PDE5-inhibitors-vardenafil has a significant effect in the treatment of Diabetic mellitus erectile dysfunction. In this systematic review, we aim to evaluate the effectiveness and safety of PDE5-inhibitors-vardenafil for Diabetic mellitus erectile dysfunction.

METHODS

We will search PubMed, Cochrane Library, AMED, EMbase, WorldSciNet; Nature, Science online and China Journal Full-text Database (CNKI), China Biomedical Literature CD-ROM Database (CBM), and related randomized controlled trials included in the China Resources Database. The time is limited from the construction of the library to February 2019.We will use the criteria provided by Cochrane 5.1.0 for quality assessment and risk assessment of the included studies, and use the Revman 5.3 and Stata13.0 software for meta-analysis of the effectiveness, recurrence rate, and symptom scores of Diabetic mellitus erectile dysfunction.

ETHICS AND DISSEMINATION

This systematic review will evaluate the efficacy and safety of PDE5-inhibitors-vardenafil for treating Diabetic mellitus erectile dysfunction. Because all of the data used in this systematic review and meta-analysis has been published, this review does not require ethical approval. Furthermore, all data will be analyzed anonymously during the review process Trial.

TRIAL REGISTRATION NUMBER

PROSPERO CRD42018095185.

Formononetin ameliorates high glucose‑induced endothelial dysfunction by inhibiting the JAK/STAT signaling pathway

High glucose‑induced endothelial Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling is associated with the development and progression of the vascular complications of diabetes. The present study aimed to investigate whether formononetin, a biologically active compound isolated from Astragalus membranaceus (Fisch.) Bge, was able to regulate the JAK/STAT signaling pathway, improving endothelial function. In the present study, formononetin was identified to act as a JAK2 inhibitor, similarly to tyrphostin AG 490 (AG490), by significantly inhibiting the phosphorylation and the mRNA expression levels of JAK2 and STAT in HUVECs exposed to high glucose levels. In addition, formononetin and AG490 improved the viability of HUVECs and inhibited the protein expression levels of caspase‑3. Furthermore, formononetin and AG490 attenuated the inflammatory response in HUVECs by downregulating the protein and mRNA expression levels of interleukin (IL)‑1β and intercellular adhesion molecule 1 (ICAM‑1). Formononetin and AG490 also restored nitric oxide (NO) synthesis in HUVECs. Notably, formononetin was able to reverse the abnormal levels of phosphorylated (p)‑JAK2, p‑STAT3, IL‑1β, ICAM‑1 and NO induced by cotreatment with high glucose and IL‑6, an agonist of the JAK/STAT signaling pathway. Additionally, the present results suggested that formononetin restored phenylephrine‑mediated contraction and acetylcholine‑induced relaxation in aortic tissues of rats fed a high‑glucose diet, in a dose‑dependent manner. Collectively, formononetin could improve endothelial function under glucose stress in vivo and in vitro, suggesting that formononetin may represent a novel potential therapeutic compound to treat diabetic vascular complications.

Traditional Chinese medicine on treating diabetic mellitus erectile dysfunction: Protocol for a systematic review and meta-analysis

BACKGROUND

Diabetic mellitus erectile dysfunction (DMED) refers to erectile dysfunction (ED) secondary to diabetes. As people's lifestyle changes and the population ages, the incidence of DMED continues to increase. Many clinical trials have proven that Chinese medicine has a significant effect in the treatment of DMED. In this systematic review, we aim to evaluate the effectiveness and safety of traditional Chinese medicine (TCM) for DMED.

METHODS

We will search PubMed, Cochrane Library, AMED, EMbase, WorldSciNet; Nature, Science online and China Journal Full-text Database, China Biomedical Literature CD-ROM Database, and related randomized controlled trials included in the China Resources Database. The time is limited from the construction of the library to February, 2019.We will use the criteria provided by Cochrane 5.1.0 for quality assessment and risk assessment of the included studies, and use the Revman 5.3 and Stata13.0 software for meta-analysis of the effectiveness, recurrence rate, and symptom scores of DMED.

ETHICS AND DISSEMINATION

This systematic review will evaluate the efficacy and safety of TCM for treating Diabetic mellitus erectile dysfunction. Because all of the data used in this systematic review and meta-analysis has been published, this review does not require ethical approval. Furthermore, all data will be analyzed anonymously during the review process trial.

A conceptual framework for predicting and addressing the consequences of disease-related microvascular dysfunction

OBJECTIVE

A growing body of evidence indicates that impaired microvascular perfusion plays a pathological role in a number of diseases. This manuscript aims to better define which aspects of microvascular perfusion are important, what mass transport processes (eg, insulin action, tissue oxygenation) may be impacted, and what therapies might reverse these pathologies.

METHODS

We derive a theory of microvascular perfusion and solute flux drawing from established relationships in mass transport and anatomy. We then apply this theory to predict relationships between microvascular perfusion parameters and microvascular solute flux.

RESULTS

For convection-limited exchange processes (eg, pulmonary oxygen uptake), our model predicts that bulk blood flow is of primary importance. For diffusion-limited exchange processes (eg, insulin action), our model predicts that perfused capillary density is of primary importance. For convection/diffusion co-limited exchange processes (eg, tissue oxygenation), our model predicts that various microvascular perfusion parameters interact in a complex, context-specific manner. We further show that our model can predict established mass transport defects in disease (eg, insulin resistance in diabetes).

CONCLUSIONS

The contributions of microvascular perfusion parameters to tissue-level solute flux can be described using a minimal mathematical model. Our results hold promise for informing therapeutic interventions targeting microvascular perfusion.

Insulin resistance adipocyte-derived exosomes aggravate atherosclerosis by increasing vasa vasorum angiogenesis in diabetic ApoE-/- mice

BACKGROUND

Vasa vasorum (VV) angiogenesis is increased in type 2 diabetes mellitus (T2DM) and may promote atherosclerotic plaque rupture. We sought to determine whether insulin resistance adipocyte-derived exosomes (IRADEs) played a major role in modulating VV angiogenesis and the mechanisms involved.

METHODS

The characterization of IRADEs was performed by electron microscopy, NTA (Nanoparticle Tracking Analysis) and western blot. The cellular effects of IRADEs on angiogenesis were explored in human umbilical vein endothelial cells (HUVECs) and murine aortic endothelial cells (MAECs) in vitro. The roles of IRADEs in angiogenesis were demonstrated with aortic ring and matrigel plug assays ex vivo and the plaque burden, plaque stability and angiogenesis-related protein expression in vivo were evaluated by ultrasonography, immunohistochemistry and western blot.

RESULTS

The IRADEs had a cup-shaped morphology, could be taken up by HUVECs and atherosclerotic plaques, and promoted tube formation by shh in vitro. In the aortic ring and matrigel plug assays, angiogenesis was significantly increased in the IRADEs group. Exogenously administered shh-containing IRADEs increased VV angiogenesis, the plaque burden, the vulnerability index and the expression of angiogenesis-related factors, whereas these effects were attenuated by silencing shh in IRADEs.

CONCLUSIONS

In conclusion, IRADEs promote plaque burden and plaque vulnerability partly by inducing VV angiogenesis, which occurs partly through shh. Accordingly, the application of IRADEs may serve as a novel therapeutic approach to treat diabetic atherosclerosis.

Prospects of Laser Doppler flowmetry application in assessment of skin microcirculation in diabetes

This review includes results of scientific and clinical use of laser Doppler flowmetry (LDF) in patients with diabetes mellitus. LDF is a non-invasive method for the quantitative evaluation of microcirculation, which can assess microcirculatory rhythms and conduct functional tests with various impacts, allowing the exploration of regulatory mechanisms of microcirculation. LDF reveals specific diabetes changes in the regulatory function of microcirculation. Microcirculation disturbances, which are traditionally associated with the pathogenesis of complications, also occur in patients with early disorders of carbohydrate metabolism and may precede the manifestation of diabetes. However, this method is still not applied in clinical practice. In this review, we analysed factors limiting the implementation of LDF in practical medicine and suggest ways to improve its clinical significance.

Coronary microvascular function in patients with type 2 diabetes mellitus

AIMS

The aims of this study were to compare the index of microcirculatory resistance (IMR) and its determinants in diabetes mellitus (DM) and non-DM patients with vascular risk factors, and to evaluate the potential differential involvement of coronary microvascular beds.

METHODS AND RESULTS

Fifty-six patients (32 with DM), without significant epicardial coronary disease, had IMR measured in the anterior and posterior circulations. There was no significant difference in the anterior compared to posterior circulation IMR in the whole group (27 vs. 26, p=0.92) or in the DM subgroup (35 vs. 28, p=0.31). DM patients had higher anterior circulation IMR compared to non-DM patients (27 vs. 15, p=0.009). Posterior circulation IMR was higher than anterior circulation IMR in non-DM patients (25 vs. 16, p=0.01). Multivariate determinants of higher anterior circulation IMR in DM were dyslipidaemia, hypertension, worsening glycaemic control, and higher body mass index; metformin had a protective effect.

CONCLUSIONS

There is differential involvement of the coronary microvascular beds. In the presence of risk factors, microvascular function of the posterior circulation was affected before the anterior; DM patients had worse microvascular function in the anterior but not posterior circulation compared to patients without DM. Vascular risk factors, including DM, adversely affect coronary microvascular function, and their treatment was associated with improvement.

Role of the Renal Microcirculation in Progression of Chronic Kidney Injury in Obesity

BACKGROUND

Obesity is largely responsible for the growing incidence and prevalence of diabetes, cardiovascular and renal diseases. Current strategies to prevent and treat obesity and its consequences have been insufficient to reverse the ongoing trends. Lifestyle modification or pharmacological therapies often produce modest weight loss which is not sustained and recurrence of obesity is frequently observed, leading to progression of target organ damage in many obese subjects. Therefore, research efforts have focused not only on the factors that regulate energy balance, but also on understanding mechanisms of target organ injury in obesity. Summary and Key Message: Microvascular (MV) disease plays a pivotal role in progressive kidney injury from different etiologies such as hypertension, diabetes, and atherosclerosis, which are all important consequences of chronic obesity. The MV networks are anatomical units that are closely adapted to specific functions of nutrition and removal of waste in every organ. Damage of the small vessels in several tissues and organs has been reported in obesity and may increase cardio-renal risk. However, the mechanisms by which obesity and its attendant cardiovascular and metabolic consequences interact to cause renal MV injury and chronic kidney disease are still unclear, although substantial progress has been made in recent years. This review addresses potential mechanisms and consequences of obesity-induced renal MV injury as well as current treatments that may provide protection of the renal microcirculation and slow progressive kidney injury in obesity.

Review: 50 years later: is metformin a vascular drug with antidiabetic properties?

Since the clinical demonstration of a protective effect of metformin against chronic diabetic angiopathy in the United Kingdom Prospective Diabetes Study, many data have accumulated which confirm such effects in acute or chronic situations as diverse as ischaemia, non-diabetic insulin resistant states and diabetes. Recent years have provided several mechanisms of action and further documented some unique properties of this compound such as improvements in microcirculatory flow, glycation and oxidative stress. In particular, the latter effect could be shown in mitochondria, i.e. the most important sources of reactive oxygen species in diabetes. Specific, non-toxic actions of metformin at the level of the mitochondrial respiratory chain also prevent apoptosis, another mechanism to explain the long-term protection afforded by metformin. Noteworthy, most of these effects of metformin are unrelated to drug dosage and largely independent of its antihyperglycaemic effect (intrinsic properties). These new data open potential avenues for larger therapeutic utilisations of this drug, 50 years after its launch for the treatment of type 2 diabetes.

Metformin attenuates hyperoxia-induced lung injury in neonatal rats by reducing the inflammatory response

Because therapeutic options are lacking for bronchopulmonary dysplasia (BPD), there is an urgent medical need to discover novel targets/drugs to treat this neonatal chronic lung disease. Metformin, a drug commonly used to lower blood glucose in type 2 diabetes patients, may be a novel therapeutic option for BPD by reducing pulmonary inflammation and fibrosis and improving vascularization. We investigated the therapeutic potential of daily treatment with 25 and 100 mg/kg metformin, injected subcutaneously in neonatal Wistar rats with severe experimental BPD, induced by continuous exposure to 100% oxygen for 10 days. Parameters investigated included survival, lung and heart histopathology, pulmonary fibrin and collagen deposition, vascular leakage, right ventricular hypertrophy, and differential mRNA expression in the lungs of key genes involved in BPD pathogenesis, including inflammation, coagulation, and alveolar development. After daily metformin treatment rat pups with experimental BPD had reduced mortality, alveolar septum thickness, lung inflammation, and fibrosis, demonstrated by a reduced influx of macrophages and neutrophils and hyperoxia-induced collagen III and fibrin deposition (25 mg/kg), as well as improved vascularization (100 mg/kg) compared with control treatment. However, metformin did not ameliorate alveolar enlargement, small arteriole wall thickening, vascular alveolar leakage, and right ventricular hypertrophy. In conclusion metformin prolongs survival and attenuates pulmonary injury by reducing pulmonary inflammation, coagulation, and fibrosis but does not affect alveolar development or prevent pulmonary arterial hypertension and right ventricular hypertrophy in neonatal rats with severe hyperoxia-induced experimental BPD.

Dual blockade of Renin Angiotensin system in reducing the early changes of diabetic retinopathy and nephropathy in a diabetic rat model

Background:

Diabetes mellitus is a real pandemic of the modern world and the incidence of the disease is increasing at a tremendous rate with a number of complications involving major systems of the human body. The renin angiotensin system (RAS) is considered to be involved in most of the pathological processes that result in diabetic nephropathy and retinopathy.

Aim:

The study was designed to evaluate and compare effects of ramipril (angiotensin-converting enzyme inhibitor-ACEI) and telmisartan (angiotensin II receptor blocker - ARBs) combinations on the progression of retinopathy and nephropathy in the streptozotocin (STZ) induced diabetic model.

Materials and Methods:

Diabetic state in rats was induced by chemical method using STZ 55 mg/kg intraperitoneally. Diabetic renal tubulopathy and interstitial inflammatory changes were done. Diabetic retinopathy manifested in the form of vacuolar changes in the inner plexiform and the ganglionic layers of the retina was observed.

Results:

Treatments with ACEI and ARBs reduced the incidence of the occurrence of cataract. The effect of combinational drugs of ACEI (ramipril) and AT1 receptor blocker (Telmisartan) was evaluated. The drugs used in combinations showed improvement in the histopathological and biochemical changes of the diabetic animals, both for the retina and kidney.

Conclusion:

The efficacy of the drugs suggests a pivotal role of the local RAS system in the pathogenesis of tubulopathy in the kidney and neuronal damage in the retina of the diabetic animals.

Protective Effect of Free and Bound Polyphenol Extracts from Ginger (Zingiber officinale Roscoe) on the Hepatic Antioxidant and Some Carbohydrate Metabolizing Enzymes of Streptozotocin-Induced Diabetic Rats

This study investigated the hepatoprotective effects of polyphenols from Zingiber officinale on streptozotocin-induced diabetic rats by assessing liver antioxidant enzymes, carbohydrate-metabolizing enzymes and liver function indices. Initial oral glucose tolerance test was conducted using 125 mg/kg, 250 mg/kg, and 500 mg/kg body weight of both free and bound polyphenols from Z. officinale. 28 day daily oral administration of 500 mg/kg body weight of free and bound polyphenols from Z. officinale to streptozotocin-induced (50 mg/kg) diabetic rats significantly reduced (P < 0.05) the fasting blood glucose compared to control groups. There was significant increase (P < 0.05) in the antioxidant enzymes activities in the animals treated with both polyphenols. Similarly, the polyphenols normalised the activities of some carbohydrate metabolic enzymes (hexokinase and phosphofructokinase) in the liver of the rats treated with it and significantly reduced (P < 0.05) the activities of liver function enzymes. The results from the present study have shown that both free and bound polyphenols from Z. officinale especially the free polyphenol could ameliorate liver disorders caused by diabetes mellitus in rats. This further validates the use of this species as medicinal herb and spice by the larger population of Nigerians.

Hepatic function and the cardiometabolic syndrome

Despite skeletal muscle being considered by many as the source of insulin resistance, physiology tells us that the liver is a central and cardinal regulator of glucose homeostasis. This is sometimes underestimated because, in contrast with muscle, investigations of liver function are technically very difficult. Nevertheless, recent experimental and clinical research has demonstrated clearly that, due in part to its anatomic position, the liver is exquisitely sensitive to insulin and other hormonal and neural factors, either by direct intrahepatic mechanisms or indirectly by organ cross-talk with muscle or adipose tissue. Because the liver receives absorbed nutrients, these have a direct impact on liver function, whether via a caloric excess or via the nature of food components (eg, fructose, many lipids, and trans fatty acids). An emerging observation with a possibly great future is the increase in intestinal permeability observed as a consequence of high fat intake or bacterial modifications in microbiota, whereby substances normally not crossing the gut gain access to the liver, where inflammation, oxidative stress, and lipid accumulation leads to fatty liver, a situation observed very early in the development of diabetes. The visceral adipose tissue located nearby is another main source of inflammatory substances and oxidative stress, and also acts on hepatocytes and Kupffer cells, resulting in stimulation of macrophages. Liberation of these substances, in particular triglycerides and inflammation factors, into the circulation leads to ectopic fat deposition and vascular damage. Therefore, the liver is directly involved in the development of the prediabetic cardiometabolic syndrome. Treatments are mainly metformin, and possibly statins and vitamin D. A very promising avenue is treatment of the leaky gut, which appears increasingly to be an important causal factor in hepatic insulin resistance and steatosis.

Investigation of the potential effects of metformin on atherothrombotic risk factors in hyperlipidemic rats

The increased mortality rate due to atherothrombotic events and related complications has necessitated the search for new pharmacological agents. Hyperlipidemia, thrombosis and oxidative stress are the primary underlying concerns in the pathogenesis of atherosclerosis. Metformin, although proved to be beneficial in micro and macrovascular complications of diabetes mellitus, its effects on pure cardiovascular subjects are still debatable. Hence, the aim of the present study was to investigate the effects of metformin on atherothrombotic risk factors in experimental hyperlipidemic rats. Hyperlipidemia was induced by an intra-peritoneal injection of criton X-100 (25 mg/kg). Assessment of the effects of metformin (300 mg/kg/day, 400 mg/kg/day and 500 mg/kg/day) on lipid profile, coagulation time (activated partial thromboplastin time and prothrombin time), fibrinogen level, thrombosis, lipid peroxidation, antioxidant enzymes level, plasma fluorescent oxidation products and aortic nitrite level revealed an overall improvement in the lipid profile at the dose of 400 mg/kg along with a significant reduction in oxidative stress as compared to criton X-100 treated control. Activated partial thromboplastin and prothrombin times were prolonged at all doses, while plasma fibrinogen level remained unaffected. Metformin pre-treatment also reduced endothelial cell damage in ferrous chloride induced thrombosis in carotid arteries. Thus, the results indicate a potential protective effect of metformin on atherothrombotic risk factors, as evident from an improvement in lipid profile, reduction in oxidative stress and thrombotic events.

Effects of a short-term improvement in glycaemic control on skin microvascular dysfunction in Type 1 and Type 2 diabetic patients

AIMS

To investigate whether Type 1 and Type 2 diabetic patients differ in the effects of short-term improvement in glycaemic control on skin microvascular dysfunction.

METHODS

Fourteen Type 1 and 14 Type 2 diabetic patients admitted to hospital to improve glycaemic control were investigated. Two age- and sex-matched groups of non-diabetic subjects served as controls. Capillary blood cell velocity (CBV) was assessed at the dorsal middle phalangeal area of the ring finger at rest and after 3-min arterial occlusion using laser Doppler anemometry.

RESULTS

Comparing the measurements before and after improvement in glycaemic control, there were no significant changes in peak CBV, time to peak CBV and vasomotion amplitudes in Type 1 and Type 2 diabetic patients. On admission to hospital, time to peak CBV was prolonged in Type 1 (20.9 +/- 2.9 vs. 12.3 +/- 1.6 s, P = 0.003) and Type 2 diabetic patients (20.6 +/- 2.6 vs. 11.9 +/- 1.3 s, P = 0.021) compared with control subjects. After improvement in glycaemic control, there was no significant difference in time to peak CBV between Type 1 diabetic patients and their control subjects (17.8 +/- 4.2 vs. 12.3 +/- 1.6 s, P = 0.535). In Type 2 diabetic patients, the time to peak CBV increased non-significantly.

CONCLUSIONS

Short-term improvement in glycaemic control did not appear to reverse microcirculatory dysfunction in Type 1 and Type 2 diabetes. However, there was an improvement of the delayed reactive hyperaemia in Type 1 diabetic patients.

The pathologic continuum of diabetic vascular disease

Hyperglycemia can promote vascular complications by multiple mechanisms, with formation of advanced glycation end products and increased oxidative stress proposed to contribute to both macrovascular and microvascular complications. Many of the earliest pathologic responses to hyperglycemia are manifest in the vascular cells that directly encounter elevated blood glucose levels. In the macrovasculature, these include endothelial cells and vascular smooth muscle cells. In the microvasculature, these include endothelial cells, pericytes (in retinopathy), and podocytes (in renal disease). Additionally, neovascularization arising from the vasa vasorum may promote atherosclerotic plaque progression and contribute to plaque rupture, thereby interconnecting macroangiopathy and microangiopathy.

The effect of metformin on measurements of insulin sensitivity and beta cell response in 18 horses and ponies with insulin resistance

REASONS FOR PERFORMING STUDY

Laminitis in equids is a very common debilitating disease, and insulin resistance (IR) and hyperinsulinaemia are increasingly recognised as important predisposing factors. Pharmacological modification of IR and hyperinsulinaemia might reduce the risk of laminitis.

HYPOTHESIS

Metformin, a drug commonly prescribed for treatment of human IR, may also decrease IR in equids.

METHODS

Eighteen horses and ponies with IR and recurrent laminitis were treated with 15 mg/kg bwt metformin per os q. 12 h. Each animal served as its own control by comparing pre- and post treatment proxies for IR, insulin sensitivity (IS) and pancreatic beta cell function while controlling for possible dietary and managemental influences on IR.

RESULTS

Evidence of significantly improved IS and decreased pancreatic beta cell secretion was found following metformin treatment. The magnitude of effect was greater at earlier resampling (6-14 days) than at later times (23-220 days). Apparent subjective clinical benefits were good but less favourable than effects on IR.

CONCLUSIONS

Metformin is safe and appears to increase IS in equids.

POTENTIAL RELEVANCE

Metformin may be indicated as a treatment for IR in equids. Further studies are required to define appropriate selection of subjects warranting therapy, dosing schedule and pharmacokinetics.

Severe obstructive sleep apnoea exacerbates the microvascular impairment in very mild hypertensives

BACKGROUND

Different studies have shown that obstructive sleep apnoea syndrome (OSAS), frequently associated with hypertension, represents a harmful and independent risk for cardiovascular diseases. The aim of our study was to ascertain whether the occurrence of OSAS could worsen microcirculatory impairment in very mild hypertensives.

MATERIALS AND METHODS

One hundred untreated very mild hypertensives underwent polysomnography and subdivided into 32 non-OSAS, 33 mild OSAS and 35 severe OSAS patients on standardized criteria. They underwent routine blood chemistry, ambulatory blood pressure monitoring and anthropometric analysis. Skin capillary density (n mm(-2)) of forearm (FAC) and periungueal (PUC) fields was obtained through videocapillaroscopy. By a venous congestion manoeuvre, PUC was maximized (CVC) and secondary capillary recruitment (GAIN) was calculated. These measurements served as indices of structural and functional capillary rarefaction, respectively.

RESULTS

Severe OSAS hypertensives showed reduced FAC (P < 0.001) and PUC (P < 0.001) as compared to those with mild OSAS and non-OSAS, but a greater CVC (P < 0.01) and GAIN (P < 0.001). Multiple regression analysis showed that PUC was inversely related to total sleep time with oxyhaemoglobin saturation at < 90% (TST90) (P < 0.001) and FAC to the apnoea-hypopnoea index (AHI) (P < 0.001) and to the sleep propensity (P < 0.01). CVC was positively associated to AHI (P < 0.001) and GAIN to TST90 (P < 0.05).

CONCLUSIONS

The findings suggest that OSAS, by means of reduced basal and functional capillarity rarefaction, might pose an additional risk of impaired peripheral perfusion in very mild hypertensives. A microcirculation study therefore should be a part of the clinical approach in patients at high cerebro-cardiovascular risk such as hypertensives and patients with OSAS.

Metformin therapy and clinical uses

Metformin is now established as a first-line antidiabetic therapy for the management of type 2 diabetes. Its early use in treatment algorithms is supported by lack of weight gain, low risk of hypoglycaemia and its mode of action to counter insulin resistance. The drug's anti-atherosclerotic and cardioprotective effects have recently been confirmed in prospective and retrospective studies, and appear to reflect a collection of glucose-independent effects on the vascular endothelium, suppressant effects on glycation, oxidative stress and formation of adhesion molecules, stimulation of fibrinolysis and favourable effects on the lipid profile. Although avoidance of troublesome gastrointestinal tolerability issues requires careful dose titration, the risk of serious adverse events is considered low provided that contra-indications (especially with respect to renal function) are observed. As many of its actions go beyond glucose lowering, emerging evidence indicates potential benefits in other insulin-resistant states and possibly tumour suppression.

[Microcirculation in diabetes: implications for chronic complications and treatment of the disease]

Diabetic microangiopathy is responsible for an important rate of morbidity and mortality related to the disease. Endothelial damage seems to be the triggering factor in the pathogenesis of microvascular complications. Diabetes mellitus and other metabolic diseases are associated to endothelial dysfunction, the most precocious known marker of atherosclerosis. Changes on microvascular reactivity are present in patients with diabetes mellitus, as well as in individuals with risk factors for this disease. Evaluation of endothelial and microvascular functions is possible using different invasive or preferentially non-invasive methods. Adequate control of diabetes mellitus might postpone or perhaps even prevent the microvascular disease. Microvascular dysfunction, when seen only by changes on microvascular reactivity, could be ameliorated with correction of risk factors or drug treatment.

Microvascular impairment is associated with insulin resistance in euglycemic mild hypertensives

BACKGROUND

Hypertension and diabetes are significantly associated with insulin resistance (IR), which could affect the vasodilatory capacity and microcirculation. The aim of the study was to verify whether IR is associated with a reduced microvascular blood flow in normoglycemic mild hypertensives.

METHODS

Eighty-four untreated grade-1 hypertensives were equally divided, according to the IR homeostasis model assessment (HOMA) index, into three groups: IR-Low = 2.16 +/- 0.09 vs. IR-Medium = 3.77 +/- 0.09 vs. IR-High = 7.08 +/- 0.68 (P < 0.001) with similar sex distribution, office systolic blood pressure (SBP)/diastolic blood pressure (DBP) and history of hypertension. They underwent ambulatory blood pressure monitoring (ABPM) and a laboratory stress session, during which blood pressure (BP), heart rate (HR), and skin blood flow (Laser Doppler) were taken on the forehead (LDF) and the hand (LDH), where the neuroadrenergic control of the microvascular blood flow is higher. Reactivity was calculated as "area-under-the-curve" (AUC) during arithmetic and cold pressor tests. Postischemic LDH served as the index of endothelial microcirculatory damage.

RESULTS

ABPM confirmed the diagnosis of hypertension, but IR-High patients showed a reduced nighttime BP fall. They also demonstrated reduced LDH-AUC and LDF-AUC although BP-AUC and HR-AUC reactivity were similar. Postischemic LDH was lower in the IR-High group (P < 0.05), and the postischemic LDH change was progressively impaired in both IR-Medium and IR-High patients (P < 0.001). LDH-AUC (-0.305, P = 0.007) and postischemic LDH at 30 s (-0.217, P = 0.059) and 60 s (-0.248, P = 0.030) during hyperemia were associated with HOMA. Multiple regression analysis, with HOMA as the dependent variable, showed that BMI (beta = 0.336, P < 0.001) and LDH (beta = -0.239, P < 0.001), LDH-AUC (beta = -0.296, P < 0.01) and postischemic LDH change (beta = -0.321, P < 0.001) entered the equation.

CONCLUSIONS

The findings suggest that IR is associated with functional microvascular constrictive impairment in normoglycemic mild hypertensives.

Longchain n-3 polyunsaturated fatty acids and microvascular reactivity: Observation in the hamster cheek pouch

Previous experiments in our laboratory, using the hamster cheek pouch microcirculation, have shown that precapillary vessels exhibit spontaneous rhythmic luminal variations, termed vasomotion, a myogenic activity sustained by a balance between membrane currents among which polarizing K(+) currents play an important role. In these microvessels, endothelium-derived relaxing factors (EDRFs) seem to regulate arteriolar diameter [via nitric oxide (NO) and cyclic GMP] and vasomotion [probably via endothelium-derived hyperpolarizing factor (EDHF)]. Fish or fish oil diet can decrease the risk of cardiovascular diseases, probably by modifying the conductance of selective ion channels, such as K(+) and/or Ca(++), and/or increasing the production of vasodilators, such as NO. To investigate its effect on microvascular reactivity, using the same preparation and an intravital microscope coupled to a closed circuit TV system, male hamsters were treated for 14 days, twice a day, with 0.4 mL/100 g body weight with fish or olive oil. An attempt was also undertaken to record in arterioles, in vivo, the membrane potential of smooth muscle cells during their vasomotor activity combining conventional microelectrode and intravital microscopy techniques. The effects of topical application of two vasodilators, acetylcholine [endothelium-dependent one, NO release and membrane hyperpolarization via Ca(++)-activated K(+) channels (K(Ca))] and sodium nitroprusside (endothelium-independent, NO donor and no change on membrane potential) and two vasoconstrictors which elicited membrane depolarization via Ca(++) channels, phenylephrine (alpha(1)-adrenergic receptor agonist) and serotonin (5-hydroxi-tryptamine) on mean internal diameter of arterioles and venules, arteriolar blood flows, spontaneous arteriolar vasomotion frequency and amplitude and functional capillary density (FCD, number of capillaries with flowing red blood cells per unit area of tissue) were determined. Anesthesia was induced by sodium pentobarbital (i.p.) and maintained with alpha-chloralose through the femoral vein. In the presence of vasomotion, the membrane potentials are slowly oscillating by about 20 mV around values of approximately -50 mV in perfect synchrony with vasomotor movements and depolarizing phases coincide with vasoconstrictions while polarizing ones with vasodilatations. Comparing all parameters, in control conditions, only the spontaneous vasomotion frequency was significantly higher (2.37 times higher) on the group treated with fish oil and persisted as such throughout all experiments. With topical application of the drugs mentioned above, the group treated with fish oil showed, for each drug concentration, a balance towards vasodilatation with consequent increase on arteriolar blood flow and on FCD, compared with the olive oil treated one. No significant changes on mean arterial pressure, spontaneous arteriolar vasomotion amplitude or venular diameter could be detected in the two groups. Our results support the concept that, in the hamster cheek pouch microcirculation, fish oil supplementation activates K(+) channels which act as the EDHF and might also increase the production of vasodilators, probably NO.

Non-invasive methods and stimuli for evaluating the skin's microcirculation

Vessels in the skin are arranged into superficial and deep horizontal plexuses and they are involved in thermoregulation, oxygen and nutritional support. The skin has a large number of functions and broad appeal spanning basic mechanistic and clinical research. Indeed, the skin can be used as a marker of normal and impaired vascular control and, owing to its accessibility and frequent involvement, is easy to investigate non-invasively. A large number of non-invasive methods are available for investigating the skin, ranging from those that permit the visualisation of microvessels, to those that monitor blood flow or one of its derivatives (e.g., skin temperature and transcutaneous oxygen). Such methods can be combined with non-invasive, dynamic stimuli (e.g., the use of cold or warm stimuli, activation of the peripheral nervous system or local neuronal systems, and the topical application of vasoactive drugs) and this potentially enables the differentiation of underlying disorders (e.g., primary from secondary Raynaud's phenomenon) and also to quantify changes over time or following intervention. The present article outlines the non-invasive methods and dynamic tests that can be used to investigate the microcirculation of the skin.

Hyperglycemia and loss of ovarian hormones mediate atheroma formation through endothelial layer disruption and increased permeability

The overall goal of this project was to examine the interactions of hyperglycemia and loss of ovarian hormones on the artery wall in a type I diabetic mouse model. Intact or ovariectomized (OVX) female BALB/C mice were fed a high-cholesterol diet. Half the animals were treated with steptozotocin to induce insulin-deficient diabetes mellitus, generating four treatment groups: control, intact; control, ovariectomized; diabetic, intact; diabetic, ovariectomized (DOVX). We examined arterial structure and function and found that 1) diabetes and ovariectomy additively increased endothelial layer permeability, 2) arterial stiffening was increased in DOVX, 3) DOVX synergistically increased atheroma formation, and 4) ultrastructural evaluation revealed that the basal lamina was often multilayered and formed convoluted aggregates separating endothelium from the internal elastic lamina in diabetic, but not control arteries or arteries from OVX mice. Endothelium overlying these regions formed thin cytoplasmic extensions between these aggregates and was often separated from the basal lamina by electron lucent spaces. Our studies showed that diabetes and loss of ovarian function have additive and synergistic effects to worsen arterial pathophysiology by disrupting the arterial endothelial layer with increased permeability and increased atheroma formation.

Reduced nitric oxide bioavailability contributes to skeletal muscle microvessel rarefaction in the metabolic syndrome

This study tested the hypothesis that chronically elevated oxidant stress contributes to impaired active hyperemia in skeletal muscle of obese Zucker rats (OZR) vs. lean Zucker rats (LZR) through progressive deteriorations in microvascular structure. Twelve-week-old LZR and OZR were given 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (tempol) in the drinking water for ∼4 wk. Subsequently, perfusion of in situ gastrocnemius muscle was determined during incremental elevations in metabolic demand, while a contralateral skeletal muscle arteriole and the gastrocnemius muscle was removed to determine dilator reactivity, vessel wall mechanics, and microvessel density. Under control conditions, active hyperemia was impaired at all levels of metabolic demand in OZR, and this was correlated with a reduced microvessel density, increased arteriolar stiffness, and impaired dilator reactivity. Chronic tempol ingestion improved perfusion during moderate to high metabolic demand only and was associated with improved arteriolar reactivity and microvessel density; passive vessel mechanics were unaltered. Combined antioxidant therapy and nitric oxide synthase inhibition in OZR prevented much of the restored perfusion and microvessel density. In LZR, treatment with Nω-nitro-l-arginine methyl ester (l-NAME) hydrochloride and hydralazine (to prevent hypertension) impaired active hyperemia, dilator reactivity, and microvessel density, although arteriolar distensibility was not altered. These results suggest that with the development of the metabolic syndrome, chronic reductions in nitric oxide bioavailability, in part via the scavenging actions of oxidative free radicals, contribute to a loss of skeletal muscle microvessels, leading to impaired muscle perfusion with elevated metabolic demand.

Metformin decreases intracellular production of reactive oxygen species in aortic endothelial cells

Beyond its antidiabetic activity justifying its use in the treatment of the type 2 diabetes, metformin (MET [dimethylguanidine, Glucophage]) has been shown to exhibit antioxidant properties in vitro, which could contribute to limit the deleterious vascular complications of diabetes. We investigated whether MET, at the pharmacological level of 10 -5 mol/L, was able to modulate intracellular production of reactive oxygen species (ROS) both in quiescent bovine aortic endothelial cells (BAECs) and in BAECs stimulated by a short incubation with high levels of glucose (30 mmol/L, 2 hours) or angiotensin II (10 -7 mol/L, 1 hour). Intracellular ROS production was measured by fluorescence of the DCF (2,7-dichlorodihydrofluorescein) probe. Our results showed that MET was able to reduce the intracellular production of ROS in both nonstimulated BAECs (-20%, P < .05) and BAEC stimulated by high levels of glucose or angiotensin II (-28% and -72%, respectively, P < .01). Experiments performed in the presence of the nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase inhibitor apocynin or the respiratory mitochondrial chain inhibitor rotenone indicated that MET exerted its effect partly through an inhibition of the formation of ROS produced mainly by NAD(P)H oxidase and also, to a lesser extent, by the respiratory mitochondrial chain.