Free fatty acids/triglycerides increase ocular and subcutaneous blood flow

Associations of retinal oximetry in persons with diabetes

BACKGROUND

There are limited data available on the variables that might affect retinal vessel oxygen saturation (SO₂) in diabetes. Therefore, the aim of this study is to assess factors associated with retinal oximetry values in persons with diabetes.

DESIGN

Clinic-based cross-sectional study.

PARTICIPANTS

Fifty-eight persons with diabetes aged 18+ years, recruited from the University of Melbourne, the Royal Victorian Eye and Ear Hospital, and St. Vincent's Hospital (Melbourne), Australia.

METHODS

Retinal oximetry was performed using the oximetry module of the Vesselmap system (Imedos UG, Jena, Germany) in 92 diabetic eyes. Generalized estimating equation models were used to estimate the associations between candidate variables (age; gender; retinal capillary flow; duration of diabetes; hypertension; smoking status; presence of diabetic retinopathy [DR]; glycated haemoglobin; triglyceride; total cholesterol; finger SO₂ and ocular perfusion pressure) with retinal oximetry measures.

MAIN OUTCOME MEASURE

Arteriolar SO₂, venular SO₂ and the arterio-venous (A-V) difference.

RESULTS

Of the candidate factors assessed, only the presence of DR was significantly associated with increased venular SO₂ and decreased A-V difference in unadjusted analyses. In models adjusting for age and gender and significant variables from unadjusted analyses, compared with no DR, the presence of DR was significantly associated with greater retinal venular SO₂ values (β = 3.65%, 95% confidence interval: 0.67-6.63%) and decreased A-V difference (β = -2.00%, 95% confidence interval: -3.46 to -0.53%).

CONCLUSION

In patients with diabetes, eyes with DR were associated with increased venular SO₂ and decreased A-V difference compared with eyes without DR, suggesting an altered metabolic state in DR.

Lipid-induced insulin resistance is not mediated by impaired transcapillary transport of insulin and glucose in humans

Increased lipid availability reduces insulin-stimulated glucose disposal in skeletal muscle, which is generally explained by fatty acid-mediated inhibition of insulin signaling. It remains unclear whether lipids also impair transcapillary transport of insulin and glucose, which could become rate controlling for glucose disposal. We hypothesized that lipid-induced insulin resistance is induced by inhibiting myocellular glucose uptake and not by interfering with the delivery of insulin or glucose. We measured changes in interstitial glucose and insulin in skeletal muscle of healthy volunteers during intravenous administration of triglycerides plus heparin or glycerol during physiologic and supraphysiologic hyperinsulinemia, by combining microdialysis with oral glucose tolerance tests and euglycemic-hyperinsulinemic clamps. Lipid infusion reduced insulin-stimulated glucose disposal by ~70% (P < 0.05) during clamps and dynamic insulin sensitivity by ~12% (P < 0.05) during oral glucose loading. Dialysate insulin and glucose levels were unchanged or even transiently higher (P < 0.05) during lipid than during glycerol infusion, whereas regional blood flow remained unchanged. These results demonstrate that short-term elevation of free fatty acids (FFAs) induces insulin resistance, which in skeletal muscle occurs primarily at the cellular level, without impairment of local perfusion or transcapillary transport of insulin and glucose. Thus, vascular effects of FFAs are not rate controlling for muscle insulin-stimulated glucose disposal.

Impact of hyperlipidaemia on the orbital bone cefotaxime levels in rats

Facial injuries are critical conditions, leading to serious complications, such as occult facial infections. Infectious endophthalmitis occurs despite of antibiotics use during implantation of intraocular lenses and is generally resistant to antibiotic therapy. It is a crucial situation in ophthalmology, since it often induces a substantial reduction of visual acuity and in some cases the loss of the eye despite treatment. It is, therefore, important to obtain drug levels able to exert antimicrobial effect in the diseased organ. The distribution of a drug depends on the binding extent to both plasma proteins and tissues and only the free drug is capable to be transported/diffused across membranes from blood vessels into tissues, in order to achieve its effect on the target organ. Hyperlipidaemia and consequent enhanced concentration of free fatty acid can modify binding pharmacokinetics of antibiotics through antagonism for the same binding sites. Cefotaxime, the third generation cephalosporin with easy penetration in a variety of tissues and body fluids and low incidence of adverse effects, can obtain adequate concentration in blood, eye bulb, and in the orbital bones. Its levels are influenced by hyperlipidaemia with clinical impact.

Arterial Stiffness and Wave Reflection: Biomarkers of Cardiovascular Risk

Arterial stiffness and excessive pressure pulsatility have emerged as important risk factors for cardiovascular disease. Arterial stiffness increases with age and in the presence of traditional cardiovascular disease risk factors, such as hypertension, diabetes and lipid disorders. Pathologic stiffening of large arteries with advancing age and risk factor exposure predominantly involves the elastic aorta and carotid arteries, whereas stiffness changes are relatively limited in muscular arteries. Aortic stiffening is associated with increased pulse wave velocity and pulse pressure, which are related but distinct measures of the pulsatile energy content of the pressure waveform. A dramatic increase in pulsatile energy content of pressure and flow waves in the arterial system places considerable pulsatile stress on the heart, large arteries and distal circulation. Large artery stiffening is associated with abnormalities in microvascular structure and function that may contribute to tissue damage, particularly in susceptible high flow organs such as the brain and kidneys. This brief review summarizes results of recent research on risk factors for and adverse effects of large artery stiffening.

Rosiglitazone prevents free fatty acid-induced vascular endothelial dysfunction

CONTEXT

Free fatty acids (FFAs) cause insulin resistance and vascular endothelial dysfunction. The peroxisome proliferator-activated receptor gamma agonist rosiglitazone acts as insulin sensitizer and could exert vasoprotective properties by preservation of endothelium-dependent vasodilation.

OBJECTIVE

We tested the effect of rosiglitazone on FFA-induced endothelial dysfunction of the forearm resistance vessels, insulin sensitivity, asymmetric dimethylarginine (ADMA), and high-sensitivity C-reactive protein concentrations in humans.

DESIGN AND SETTING

We conducted a double-blind, randomized, placebo-controlled parallel-group study at a university hospital.

PATIENTS AND INTERVENTIONS

Rosiglitazone 8 mg daily or placebo was administered to 16 healthy male subjects for 21 d. On the last day, triglycerides and heparin were infused iv to increase FFA plasma concentrations.

MAIN OUTCOME MEASURES

Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine and the endothelium-independent vasodilator nitroglycerine were assessed using strain-gauge plethysmography at baseline, and on d 21 before and after 5 h of triglyceride/heparin infusion.

RESULTS

Forearm blood flow reactivity was not affected by rosiglitazone or placebo. Infusion of triglyceride/heparin substantially increased FFA concentrations (P < 0.001) and reduced endothelium-dependent vasodilation by 38 +/- 17% (P = 0.024). In the face of lower FFA elevation (P = 0.047 vs. controls), endothelium-dependent vasodilation was preserved in subjects receiving rosiglitazone (P = 0.016 vs. placebo). Endothelium-independent vasodilation and C-reactive protein were unchanged, whereas insulin sensitivity and plasma ADMA similarly decreased in both study groups after FFA elevation (both P < 0.05 vs. baseline).

CONCLUSIONS

Rosiglitazone mitigates the increase in FFA after infusion of triglyceride/heparin and prevents FFA-induced endothelial dysfunction. These effects are independent and possibly occur before any changes in insulin sensitivity and ADMA plasma concentrations in healthy subjects.

Molecular mechanisms of lipid-induced insulin resistance in muscle, liver and vasculature

Increased body fat content correlates with insulin resistance and is a key feature of type 2 diabetes. Excessive intake of fat results in deposition of lipids not only in fat tissue but also in skeletal muscle and liver. Subsequently, both plasma and intracellular concentrations of free fatty acids and their metabolites rise and activate signal transduction pathways, which will induce inflammation and impair insulin signalling. Furthermore, elevated circulating lipids impair endothelial function and fibrinolysis, which contributes to the development of vascular disease. Thus, therapeutic strategies aiming at reduction of (intracellular) lipid availability in skeletal muscle and liver and pharmacological modulation of the signalling pathways activated by increased lipid stores represent promising targets for future treatment of insulin resistance and prevention of its complications. This review focuses on the effects of increased lipid availability on the regulation of glucose metabolism in skeletal muscle and liver as well as on vascular function.

Free fatty acids exert a greater effect on ocular and skin blood flow than triglycerides in healthy subjects

BACKGROUND

Free fatty acids (FFAs) and triglycerides (TGs) can cause vascular dysfunction and arteriosclerosis. Acute elevation of plasma FFA and TG concentration strongly increase ocular and skin blood flow. This study was designed to discriminate whether FFA or TG independently induce hyperperfusion by measuring regional and systemic haemodynamics.

METHODS

In a balanced, randomized, placebo-controlled, double-blind, three-way, crossover study nine healthy subjects received either Intralipid (Pharmacia and Upjohn, Vienna, Austria) with heparin, Intralipid alone or placebo control. Pulsatile choroidal blood flow was measured with laser interferometry, retinal blood flow and retinal red blood cell velocity with laser Doppler velocimetry, and skin blood flow with laser Doppler flowmetry during an euglycaemic insulin clamp.

RESULTS

A sevenfold increase of FFA during Intralipid/heparin infusion was paralleled by enhanced choriodal, retinal, and skin blood flow by 17 +/- 4%, 26 +/- 5% (P < 0.001), and 47 +/- 19% (P = 0.03) from baseline, respectively. In contrast, a mere threefold increase of FFA by infusion of Intralipid alone did not affect outcome parameters, despite the presence of plasma TG levels of 250-700 mg dL(-1); similar to those obtained during combined Intralipid/heparin infusion. Systemic haemodynamics were not affected by drug infusion.

CONCLUSIONS

Present findings demonstrate a concentration-dependent increase in ocular and skin blood flow by FFA independently of elevated TG plasma concentrations. As vasodilation of resistance vessels occur rapidly, FFA may play a role in the development of continued regional hyperperfusion and deteriorate microvascular function.

The S447X polymorphism of the lipoprotein lipase gene is associated with lipoprotein lipid and blood pressure levels in Chinese patients with essential hypertension

OBJECTIVE

To investigate the association between the S447X polymorphism of the lipoprotein lipase (LPL) gene and lipoprotein lipid and blood pressure (BP) levels in 904 Chinese subjects with essential hypertension.

METHOD

Five hundred and sixty-three male and 341 female patients (aged 35-69 years) were randomly selected from hypertensive patients diagnosed in the Community-based Comprehensive Studies on Prevention and Control of Hypertension Project in China (CCPACH) and not treated with antihypertensive medications for at least 2 weeks immediately before blood collection.

RESULTS

After multivariate adjustment for age, body mass index (BMI), smoking status, alcohol intake and serum glucose, the X447 allele was significantly associated with low triglyceride, log triglyceride : high-density lipoprotein (HDL)-cholesterol ratio and high HDL-cholesterol levels compared with the S447S genotype, but not with BP levels in the whole study population. However, upon stratification for dyslipidemic status, the X447 allele was associated with higher systolic blood pressure (SBP) (P < 0.05) and pulse pressure (PP) (P < 0.05) compared with the S447S genotype after multivariate adjustment in dyslipidemic subjects, but not in those without dyslipidemia. A statistically significant interaction between the LPL S447X polymorphism and dyslipidemic status was observed for SBP and PP levels, suggesting that dyslipidemic status might modify the effect of the LPL S447X polymorphism on BP levels.

CONCLUSIONS

Our findings suggest that a high concentration of triglyceride and/or low concentration of HDL-cholesterol are associated with high SBP and PP in hypertensive patients with the X447 allele of the LPL gene.

Association of the D8S282 marker near the lipoprotein lipase gene locus with systolic blood pressure in healthy Chinese subjects

OBJECTIVE

To investigate the association between the marker D8S282 near the lipoprotein lipase (LPL) gene locus, and blood pressure, anthropometric and biochemical parameters in 229 healthy Chinese subjects. METHOD Genotyping was performed using an automated DNA sequencer and the Base ImageIR software. Eight different alleles were identified (272-286 bp) resulting in 15 genotypes in our population. We investigated the association between the common (28.8%) 278 bp allele and the anthropometric and biochemical parameters.

RESULTS

In a tertile analysis, the frequency of the 278 bp allele increased linearly ( P = 0.003) with increasing systolic blood pressure (SBP). The relationship was most evident in the females ( n = 141); SBP was higher in homozygotes for the 278 bp allele (117 +/- 10 mmHg, = 12) than those without this allele (109 +/- 9 mmHg, = 77, 0.05) and was gene-dose dependent, and this difference was more significant after adjusting for age (P = 0.004). No relationship between the locus and the anthropometric or biochemical parameters investigated was observed.

CONCLUSION

The D8S282 marker near the LPL gene locus contributes to the variance of SBP in healthy Hong Kong Chinese subjects, particularly in females.

Hemodynamic effects of lipids in humans

Evidence suggests lipid abnormalities may contribute to elevated blood pressure, increased vascular resistance, and reduced arterial compliance among insulin-resistant subjects. In a study of 11 normal volunteers undergoing 4-h-long infusions of Intralipid and heparin to raise plasma nonesterified fatty acids (NEFAs), we observed increases of blood pressure. In contrast, blood pressure did not change in these same volunteers during a 4-h infusion of saline and heparin. To better characterize the hemodynamic responses to Intralipid and heparin, another group of 21 individuals, including both lean and obese volunteers, was studied after 3 wk on a controlled diet with 180 mmol sodium/day. Two and four hours after starting the infusions, plasma NEFAs increased by 134 and 111% in those receiving Intralipid and heparin, P < 0.01, whereas plasma NEFAs did not change in the first group of normal volunteers who received saline and heparin. The hemodynamic changes in lean and obese subjects in the second study were similar, and the results were combined. The infusion of Intralipid and heparin induced a significant increase in systolic (13.5 +/- 2.1 mmHg) and diastolic (8.0 +/- 1.5 mmHg) blood pressure as well as heart rate (9.4 +/- 1.4 beats/min). Small and large artery compliance decreased, and systemic vascular resistance rose. These data raise the possibility that lipid abnormalities associated with insulin resistance contribute to the elevated blood pressure and heart rate as well as the reduced vascular compliance observed in subjects with the cardiovascular risk factor cluster.