Intralipid enhances alpha1-adrenergic receptor mediated pressor sensitivity

Effects of Intravenous Lipid Emulsion Administration in Acute Tramadol Poisoning: A Randomized Controlled Trial

BACKGROUND

As the prevalence of tramadol toxicity is increasing, managing these patients with the aim of treatment and complete recovery has become a major challenge for health care professionals.

OBJECTIVE

This study evaluated the short-term effects of IV lipid emulsion (ILE) administration in cases of tramadol poisoning.

METHODS

In this double-blind, randomized controlled trial, 120 patients with pure tramadol poisoning and a Glasgow Coma (GCS) score ≤ 12 referred to a poisoning center in Tehran, Iran were selected and randomly assigned 1:1 to receive ILE 20% (intervention) or 0.9% saline (control) after admission and primary stabilization. The patient's vital signs, GCS score, hospitalization duration, and rate of seizure occurrence were recorded and compared between the two groups.

RESULTS

Mean (SD) age of participants was 25.3 (5.4) years and 84 (70%) were male. Mean (SD) ingested dose of tramadol was 3118 (244) mg, which was not different between the groups. Compared with controls, the ILE group had a higher level of consciousness after treatment (median [interquartile range] GCS score 12 [10-13] vs. 10 [8-12]; p = 0.03). In addition, length of hospitalization (median [interquartile range] (2 [1-3] days vs. 4 [4-6] days; p < 0.01) and rate of seizure occurrence were lower in the intervention group (16/60 vs. 30/60; p < 0.01).

CONCLUSIONS

In the setting of tramadol poisoning with a decreased level of consciousness and based on our study's findings, administration of ILE is suggested to help manage patients in hospital emergency departments. However, larger trials might be needed to confirm these findings before entering the guidelines.

Brain Dopamine-Clock Interactions Regulate Cardiometabolic Physiology: Mechanisms of the Observed Cardioprotective Effects of Circadian-Timed Bromocriptine-QR Therapy in Type 2 Diabetes Subjects

Despite enormous global efforts within clinical research and medical practice to reduce cardiovascular disease(s) (CVD), it still remains the leading cause of death worldwide. While genetic factors clearly contribute to CVD etiology, the preponderance of epidemiological data indicate that a major common denominator among diverse ethnic populations from around the world contributing to CVD is the composite of Western lifestyle cofactors, particularly Western diets (high saturated fat/simple sugar [particularly high fructose and sucrose and to a lesser extent glucose] diets), psychosocial stress, depression, and altered sleep/wake architecture. Such Western lifestyle cofactors are potent drivers for the increased risk of metabolic syndrome and its attendant downstream CVD. The central nervous system (CNS) evolved to respond to and anticipate changes in the external (and internal) environment to adapt survival mechanisms to perceived stresses (challenges to normal biological function), including the aforementioned Western lifestyle cofactors. Within the CNS of vertebrates in the wild, the biological clock circuitry surveils the environment and has evolved mechanisms for the induction of the obese, insulin-resistant state as a survival mechanism against an anticipated ensuing season of low/no food availability. The peripheral tissues utilize fat as an energy source under muscle insulin resistance, while increased hepatic insulin resistance more readily supplies glucose to the brain. This neural clock function also orchestrates the reversal of the obese, insulin-resistant condition when the low food availability season ends. The circadian neural network that produces these seasonal shifts in metabolism is also responsive to Western lifestyle stressors that drive the CNS clock into survival mode. A major component of this natural or Western lifestyle stressor-induced CNS clock neurophysiological shift potentiating the obese, insulin-resistant state is a diminution of the circadian peak of dopaminergic input activity to the pacemaker clock center, suprachiasmatic nucleus. Pharmacologically preventing this loss of circadian peak dopaminergic activity both prevents and reverses existing metabolic syndrome in a wide variety of animal models of the disorder, including high fat-fed animals. Clinically, across a variety of different study designs, circadian-timed bromocriptine-QR (quick release) (a unique formulation of micronized bromocriptine-a dopamine D2 receptor agonist) therapy of type 2 diabetes subjects improved hyperglycemia, hyperlipidemia, hypertension, immune sterile inflammation, and/or adverse cardiovascular event rate. The present review details the seminal circadian science investigations delineating important roles for CNS circadian peak dopaminergic activity in the regulation of peripheral fuel metabolism and cardiovascular biology and also summarizes the clinical study findings of bromocriptine-QR therapy on cardiometabolic outcomes in type 2 diabetes subjects.

Lipid Emulsion to Treat Acute Poisonings: Mechanisms of Action, Indications, and Controversies

Biodetoxification using intravenous lipid emulsion (ILE) in acute poisoning is of growing interest. As well as for local anesthetics, ILE is currently used to reverse toxicity caused by a broad-spectrum of lipophilic drugs. Both pharmacokinetic and pharmacodynamic mechanisms have been postulated to explain its possible benefits, mainly combining a scavenging effect called "lipid sink" and cardiotonic activity. Additional mechanisms based on ILE-attributed vasoactive and cytoprotective properties are still under investigation. Here, we present a narrative review on lipid resuscitation, focusing on the recent literature with advances in understanding ILE-attributed mechanisms of action and evaluating the evidence supporting ILE administration that enabled the international recommendations. Many practical aspects are still controversial, including the optimal dose, the optimal administration timing, and the optimal duration of infusion for clinical efficacy, as well as the threshold dose for adverse effects. Present evidence supports the use of ILE as first-line therapy to reverse local anesthetic-related systemic toxicity and as adjunct therapy in lipophilic non-local anesthetic drug overdoses refractory to well-established antidotes and supportive care. However, the level of evidence is low to very low, as for most other commonly used antidotes. Our review presents the internationally accepted recommendations according to the clinical poisoning scenario and provides the precautions of use to optimize the expected efficacy of ILE and limit the inconveniences of its futile administration. Based on their absorptive properties, the next generation of scavenging agents is additionally presented. Although emerging research shows great potential, several challenges need to be overcome before parenteral detoxifying agents could be considered as an established treatment for severe poisonings.

Lipid emulsions in the treatment of intoxications by local anesthesics and other drugs. Review of mechanisms of action and recommendations for use

Intravenous lipid emulsions (ILEs) have been used widely for the treatment of local anesthetic (LA) poisoning and have been proposed as a treatment for intoxication by other drugs. However, the degree of evidence for this kind of therapy is not strong, as it comes mostly from clinical cases. The aim of this narrative review is to describe the proposed mechanisms of action for ILEs in poisoning by LA and other drugs and to evaluate recent studies in animals that support the recommendations for their use and the experience in humans that support the use of ILESs in both LA and other drug poisoning. For this purpose, a search was performed in the Embase, Medline and Google Scholar databases covering relevant articles over the last 10 years. In the case of AL poisoning, we recommend applying the protocols dictated by international guidelines, knowing that the degree of evidence is not very high. In poisoning by other drugs, ILEs are recommended in serious situations induced by liposoluble xenobiotics that do not respond to standard treatment.

Lipid emulsions in the treatment of intoxications by local anesthesics and other drugs. Review of mechanisms of action and recommendations for use

Intravenous lipid emulsions (ILEs) have been used widely for the treatment of local anesthetic (LA) poisoning and have been proposed as a treatment for intoxication by other drugs. However, the degree of evidence for this kind of therapy is not strong, as it comes mostly from clinical cases. The aim of this narrative review is to describe the proposed mechanisms of action for ILEs in poisoning by LA and other drugs and to evaluate recent studies in animals that support the recommendations for their use and the experience in humans that support the use of ILESs in both LA and other drug poisoning. For this purpose, a search was performed in the Embase, Medline and Google Scholar databases covering relevant articles over the last 10 years. In the case of AL poisoning, we recommend applying the protocols dictated by international guidelines, knowing that the degree of evidence is not very high. In poisoning by other drugs, ILEs are recommended in serious situations induced by liposoluble xenobiotics that do not respond to standard treatment.

Nonesterified Fatty Acids and Kidney Function Decline in Older Adults: Findings From the Cardiovascular Health Study

RATIONALE & OBJECTIVE

Circulating nonesterified fatty acids (NEFAs) make up a small portion of circulating lipids but are a metabolically important energy source. Excessive circulating NEFAs may contribute to lipotoxicity in many tissues, including the kidneys. We investigated the relationship between total circulating NEFA concentration and kidney outcomes in older, community-dwelling adults.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

4,698 participants≥65 years of age in the Cardiovascular Health Study who underwent total fasting serum NEFA concentration measurements in 1992-1993.

EXPOSURE

Fasting serum NEFA concentration at one time point.

OUTCOME

Three primary outcomes: estimated glomerular filtration rate (eGFR) decline of≥30%, the composite of eGFR decline≥30% or kidney failure with replacement therapy, and change in eGFR. These outcomes were assessed over 4- and 13-year periods.

ANALYTICAL APPROACH

Logistic regression for the dichotomous outcomes and mixed effects models for the continuous outcome, with sequential adjustment for baseline covariates. Inverse probability of attrition weighting was implemented to account for informative attrition during the follow-up periods.

RESULTS

Serum NEFA concentrations were not independently associated with kidney outcomes. In unadjusted and partially adjusted analyses, the highest quartile of serum NEFA concentration (compared with lowest) was associated with a higher risk of≥30% eGFR decline at 4 years and faster rate of decline of eGFR. No associations were evident after adjustment for comorbidities, lipid levels, insulin sensitivity, medications, and vital signs: the odds ratio for the eGFR decline outcome was 1.33 (95% CI, 0.83-2.13), and the difference in eGFR slope in the highest versus lowest quartile of serum NEFA concentration was-0.15 (95% CI, -0.36 to 0.06) mL/min/1.73m² per year.

LIMITATIONS

Single NEFA measurements, no measurements of post-glucose load NEFA concentrations or individual NEFA species, no measurement of baseline urine albumin.

CONCLUSIONS

A single fasting serum NEFA concentration was not independently associated with long-term adverse kidney outcomes in a cohort of older community-living adults.

Linolenic acid enhances contraction induced by phenylephrine in isolated rat aorta

This study examined the effect of linolenic acid on the contraction of isolated endothelium-intact and -denuded rat aorta induced by phenylephrine and its underlying mechanism. This was conducted in the presence or absence of N^W-nitro-L-arginine methyl ester (L-NAME), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), methylene blue, and calmidazolium. The effects of linolenic acid on contraction induced by calcium chloride in calcium-free Krebs solution containing 60 mM potassium chloride were also examined. Moreover, the effect of linolenic acid on the association between intracellular calcium level ([Ca²⁺]_i) and tension induced by phenylephrine was examined. Finally, we examined the effects of linolenic acid on cGMP formation and endothelial nitric oxide synthase (eNOS) phosphorylation induced by phenylephrine. Linolenic acid (5 × 10^-5 M) increased phenylephrine-induced contraction in endothelium-intact aorta (standardized mean difference [SMD] of log ED₅₀: 2.23), whereas it decreased this contraction in endothelium-denuded aorta (SMD: 1.96). L-NAME, ODQ, methylene blue, and calmidazolium increased phenylephrine-induced contraction in endothelium-intact aorta. Linolenic acid decreased contraction induced by calcium chloride in calcium-free Krebs solution containing 60 mM potassium chloride in endothelium-denuded aorta. Linolenic acid caused an increase in [Ca²⁺]_i (SMD at 3 × 10^-7 M phenylephrine: 1.63) and calcium sensitivity induced by phenylephrine in endothelium-intact aorta. Conversely, linolenic acid decreased [Ca²⁺]_i (SMD: 0.99) induced by phenylephrine in endothelium-denuded aorta. Linolenic acid decreased cGMP formation and eNOS phosphorylation induced by phenylephrine. These results suggest that linolenic acid increases phenylephrine-induced contraction, which is attributed to linolenic acid inhibition of endothelial NO release rather than its decrease of [Ca²⁺]_i in vascular smooth muscle.

The Mechanisms Underlying Lipid Resuscitation Therapy

The experimental use of lipid emulsion for local anesthetic toxicity was originally identified in 1998. It was then translated to clinical practice in 2006 and expanded to drugs other than local anesthetics in 2008. Our understanding of lipid resuscitation therapy has progressed considerably since the previous update from the American Society of Regional Anesthesia and Pain Medicine, and the scientific evidence has coalesced around specific discrete mechanisms. Intravenous lipid emulsion therapy provides a multimodal resuscitation benefit that includes both scavenging (eg, the lipid shuttle) and nonscavenging components. The intravascular lipid compartment scavenges drug from organs susceptible to toxicity and accelerates redistribution to organs where drug (eg, bupivacaine) is stored, detoxified, and later excreted. In addition, lipid exerts nonscavenging effects that include postconditioning (via activation of prosurvival kinases) along with cardiotonic and vasoconstrictive benefits. These effects protect tissue from ischemic damage and increase tissue perfusion during recovery from toxicity. Other mechanisms have diminished in favor based on lack of evidence; these include direct effects on channel currents (eg, calcium) and mass-effect overpowering a block in mitochondrial metabolism. In this narrative review, we discuss these proposed mechanisms and address questions left to answer in the field. Further work is needed, but the field has made considerable strides towards understanding the mechanisms.

The effects of intravenous lipid emulsion on hemodynamic recovery and myocardial cell mitochondrial function after bupivacaine toxicity in anesthetized pigs

Local anesthetic toxicity is thought to be mediated partly by inhibition of cardiac mitochondrial function. Intravenous (i.v.) lipid emulsion may overcome this energy depletion, but doses larger than currently recommended may be needed for rescue effect. In this randomized study with anesthetized pigs, we compared the effect of a large dose, 4 mL/kg, of i.v. 20% Intralipid® ( n = 7) with Ringer’s acetate ( n = 6) on cardiovascular recovery after a cardiotoxic dose of bupivacaine. We also examined mitochondrial respiratory function in myocardial cell homogenates analyzed promptly after needle biopsies from the animals. Bupivacaine plasma concentrations were quantified from plasma samples. Arterial blood pressure recovered faster and systemic vascular resistance rose more rapidly after Intralipid than Ringer’s acetate administration ( p < 0.0001), but Intralipid did not increase cardiac index or left ventricular ejection fraction. The lipid-based mitochondrial respiration was stimulated by approximately 30% after Intralipid ( p < 0.05) but unaffected by Ringer’s acetate. The mean (standard deviation) area under the concentration–time curve (AUC) of total bupivacaine was greater after Intralipid (105.2 (13.6) mg·min/L) than after Ringer’s acetate (88.1 (7.1) mg·min/L) ( p = 0.019). After Intralipid, the AUC of the lipid-un-entrapped bupivacaine portion (97.0 (14.5) mg·min/L) was 8% lower than that of total bupivacaine ( p < 0.0001). To conclude, 4 mL/kg of Intralipid expedited cardiovascular recovery from bupivacaine cardiotoxicity mainly by increasing systemic vascular resistance. The increased myocardial mitochondrial respiration and bupivacaine entrapment after Intralipid did not improve cardiac function.

Metabolic syndrome: a sympathetic disease?

Metabolic syndrome is associated with adverse health outcomes and is a growing problem worldwide. Although efforts to harmonise the definition of metabolic syndrome have helped to better understand the prevalence and the adverse outcomes associated with the disorder on a global scale, the mechanisms underpinning the metabolic changes that define it are incompletely understood. Accumulating evidence from laboratory and human studies suggests that activation of the sympathetic nervous system has an important role in metabolic syndrome. Indeed, treatment strategies commonly recommended for patients with metabolic syndrome, such as diet and exercise to induce weight loss, are associated with sympathetic inhibition. Pharmacological and device-based approaches to target activation of the sympathetic nervous system directly are available and have provided evidence to support the important part played by sympathetic regulation, particularly for blood pressure and glucose control. Preliminary evidence is encouraging, but whether therapeutically targeting sympathetic overactivity could help to prevent metabolic syndrome and attenuate its adverse outcomes remains to be determined.

Relevance of Sympathetic Nervous System Activation in Obesity and Metabolic Syndrome

Sympathetic tone is well recognised as being implicit in cardiovascular control. It is less readily acknowledged that activation of the sympathetic nervous system is integral in energy homeostasis and can exert profound metabolic effects. Accumulating data from animal and human studies suggest that central sympathetic overactivity plays a pivotal role in the aetiology and complications of several metabolic conditions that can cluster to form the Metabolic Syndrome (MetS). Given the known augmented risk for type 2 diabetes, cardiovascular disease, and premature mortality associated with the MetS understanding the complex pathways underlying the metabolic derangements involved has become a priority. Many factors have been proposed to contribute to increased sympathetic nerve activity in metabolic abnormalities including obesity, impaired baroreflex sensitivity, hyperinsulinemia, and elevated adipokine levels. Furthermore there is mounting evidence to suggest that chronic sympathetic overactivity can potentiate two of the key metabolic alterations of the MetS, central obesity and insulin resistance. This review will discuss the regulatory role of the sympathetic nervous system in metabolic control and the proposed pathophysiology linking sympathetic overactivity to metabolic abnormalities. Pharmacological and device-based approaches that target central sympathetic drive will also be discussed as possible therapeutic options to improve metabolic control in at-risk patient cohorts.

Intravenous lipid emulsion alters the hemodynamic response to epinephrine in a rat model

Intravenous lipid emulsion (ILE) is an adjunctive antidote used in selected critically ill poisoned patients. These patients may also require administration of advanced cardiac life support (ACLS) drugs. Limited data is available to describe interactions of ILE with standard ACLS drugs, specifically epinephrine. Twenty rats with intra-arterial and intravenous access were sedated with isoflurane and split into ILE or normal saline (NS) pretreatment groups. All received epinephrine 15 μm/kg intravenously (IV). Continuous mean arterial pressure (MAP) and heart rate (HR) were monitored until both indices returned to baseline. Standardized t tests were used to compare peak MAP, time to peak MAP, maximum change in HR, time to maximum change in HR, and time to return to baseline MAP/HR. There was a significant difference (p = 0.023) in time to peak MAP in the ILE group (54 s, 95 % CI 44-64) versus the NS group (40 s, 95 % CI 32-48) and a significant difference (p = 0.004) in time to return to baseline MAP in ILE group (171 s, 95 % CI 148-194) versus NS group (130 s, 95 % CI 113-147). There were no significant differences in the peak change in MAP, peak change in HR, time to minimum HR, or time to return to baseline HR between groups. ILE-pretreated rats had a significant difference in MAP response to epinephrine; ILE delayed the peak effect and prolonged the duration of effect of epinephrine on MAP, but did not alter the peak increase in MAP or the HR response.

Plasma free fatty acids and risk of stroke in the Cardiovascular Health Study

BACKGROUND

Although free fatty acids have been positively associated with risk factors for stroke, the role of plasma free fatty acids in the development of stroke has not been elucidated in older adults.

AIMS

We sought to examine the association between plasma free fatty acids and incident stroke.

METHODS

Prospective cohort of 4369 men and women≥65 years of age in the Cardiovascular Health Study. Plasma levels of free fatty acids were measured at the 1992-1993 examination and stroke events were adjudicated by a committee of experts including neurologists and neuroradiologists. Cox regression was used to estimate the relative risk of stroke associated with free fatty acids concentrations.

RESULTS

The average age among participants was 75±5·2 years. During a median follow-up of 11·4 years, 732 incident strokes occurred. The crude incidence rates of stroke were 14·5, 14·9, and 17·6 per 1000 person-years across increasing tertiles of plasma free fatty acids. The adjusted hazard ratio (95% confidence interval) for incident stroke was 1·05 (0·97-1·14) per standard deviation increase in plasma free fatty acids. Restriction to ischemic stroke did not alter the results [hazard ratio (95% confidence interval): 1·04 (0·96-1·14) per standard deviation higher free fatty acids], and there was no effect modification by adiposity (P interaction=0·18) or by diabetes (P interaction=0·15).

CONCLUSION

Our data did not show an association of plasma free fatty acids with incident stroke among community dwelling older adults.

Clustering of the metabolic syndrome components in adolescence: role of visceral fat

Visceral fat (VF) promotes the development of metabolic syndrome (MetS), which emerges as early as in adolescence. The clustering of MetS components suggests shared etiologies, but these are largely unknown and may vary between males and females. Here, we investigated the latent structure of pre-clinical MetS in a community-based sample of 286 male and 312 female adolescents, assessing their abdominal adiposity (VF) directly with magnetic resonance imaging. Principal component analysis of the five MetS-defining variables (VF, blood pressure [BP], fasting serum triglycerides, HDL-cholesterol and glucose) identified two independent components in both males and females. The first component was sex-similar; it explained >30% of variance and was loaded by all but BP variables. The second component explained >20% of variance; it was loaded by BP similarly in both sexes but additional loading by metabolic variables was sex-specific. This sex-specificity was not detected in analyses that used waist circumference instead of VF. In adolescence, MetS-defining variables cluster into at least two sub-syndromes: (1) sex-similar metabolic abnormalities of obesity-induced insulin resistance and (2) sex-specific metabolic abnormalities associated with BP elevation. These results suggest that the etiology of MetS may involve more than one pathway and that some of the pathways may differ between males and females. Further, the sex-specific metabolic abnormalities associated with BP elevation suggest the need for sex-specific prevention and treatment strategies of MetS.

Lipid emulsion combined with epinephrine and vasopressin does not improve survival in a swine model of bupivacaine-induced cardiac arrest

BACKGROUND

This study sought to evaluate the efficacy of lipid emulsion in reversing bupivacaine-induced cardiovascular collapse when added to a resuscitation protocol that included the use of epinephrine and vasopressin.

METHODS

After induction of general anesthesia and instrumentation, 19 mixed-breed domestic swine had cardiovascular collapse induced by an intravenous bolus of 10 mg/kg bupivacaine. After 5 min of resuscitation including chest compressions, epinephrine (100 microg/kg) and vasopressin (1.5 U/kg), animals were randomized to receive either a bolus of 20% lipid emulsion (4 ml/kg) followed by a continuous infusion (0.5 ml x kg(-1) x min(-1)) or an equal volume of saline. Investigators were blinded to the treatment assignment. The primary endpoint was return of spontaneous circulation (mean arterial pressure of at least 60 mmHg for at least 1 min).

RESULTS

Treatment groups were similar with respect to baseline measurements of weight, sex, and hemodynamic and metabolic variables. The rates of return of spontaneous circulation were similar between groups: (3 of 10) in the lipid group and 4 of 9 in the saline group (P = 0.65). Total serum bupivacaine concentrations were higher in the lipid group at the 10-min timepoint (mean +/- SEM: 23.13 +/- 5.37 ng/ml vs. 15.33 +/- 4.04 ng/ml, P = 0.004). More norepinephrine was required in the lipid group compared to the saline group to maintain a mean arterial pressure above 60 mmHg during the 60-min survival period (mean +/- SEM: 738.6 +/- 94.4 vs.. 487.3 +/- 171.0 microg).

CONCLUSIONS

In this swine model, lipid emulsion did not improve rates of return of spontaneous circulation after bupivacaine-induced cardiovascular collapse.

Effects of acute hypercholesterolemia on blood pressure and pressor response to norepinephrine in rats

To examine if high cholesterol in blood acutely affects the blood pressure, we partly exchanged the blood of normal rats for that of hypercholesterolemic rats. Male Sprague-Dawley rats were fed for 8 weeks with a high-cholesterol diet (4% cholesterol; HC) or a normal diet (NC). The rats were catheterized; and blood of animals in NC was partly exchanged with that of HC (N-H) or other animals in NC (N-N). Systolic blood pressure (SBP) and the pressor response to norepinephrine (NE) in N-H were compared with those of N-N. Serum lipids and malondialdehyde (MDA), and urinary excretion of protein (UP) and NE (UNE) were determined. After 8 weeks, SBP, serum total cholesterol (TC), MDA, UP and UNE were higher in the HC. Blood exchange caused an increase in TC, MDA and SBP in only the N-H. Increases in SBP caused by NE injection were rather less in the N-H than in the N-N. The blood pressure increase induced by a high-cholesterol diet seemed to be caused by certain factors in the blood of hypercholesterolemic rats. Excessive lipid oxidation induced by hypercholesterolemia may be involved in the blood pressure elevation.

Effect of Sex Hormones on Non-Esterified Fatty Acids, Intra-Abdominal Fat Accumulation, and Hypertension Induced by Sucrose Diet in Male Rats

Sucrose-fed rats (1) had higher intra-abdominal fat mass and plasma non-esterified fatty acids and lower testosterone levels, (2) were hypertensive, and (3) had lower plasma NO metabolites than controls. The lack of testosterone by castration of sucrose-fed rats decreased high blood pressure and circulating non-esterified fatty acids and increased NO metabolites. The administration of testosterone to castrated sucrose-fed rats restored hypertension, fat accumulation, and high-circulating non-esterified fatty acids, and lowered NO metabolite levels whereas estradiol treatment did not significantly affect these variables in castrated animals. This study proposes that the low levels of testosterone found in sucrose-fed rats are sufficient to maintain central obesity and increased circulating non-esterified fatty acids, which contribute to the development of hypertension in sucrose-fed rats by modulating the biosynthesis of NO.

Non-esterified fatty acids and blood pressure elevation: a mechanism for hypertension in subjects with obesity/insulin resistance?

The prevalence of hypertension in individuals with obesity or type II diabetes is substantially elevated. Increased levels of non-esterified fatty acids (NEFAs) in abdominally obese subjects were reported to contribute in the development of various disturbances related to the metabolic syndrome, such as hepatic and peripheral insulin resistance (IR), dyslipidaemia, beta-cell apoptosis, endothelial dysfunction and others. However, the involvement of NEFAs in the development of hypertension has been much less studied in comparison to other mechanisms linking IR and central obesity with blood pressure (BP) elevation. This article reviews the existing evidence on the relation between NEFA and hypertension in an attempt to shed a light on it. In vivo data from both animal and human studies support that acute plasma NEFA elevation leads to increase in BP levels, whereas epidemiological evidence suggests a link between increased NEFA levels and hypertension. Further, accumulating data indicate the existence of several pathways through which NEFAs could promote BP elevation, that is alpha(1)-adrenergic stimulation, endothelial dysfunction, increase in oxidant stress, stimulation of vascular cell's growth and others. The above data support a possible important role of NEFA in hypertension development in patients with obesity and the metabolic syndrome and raise hypotheses for future research.

Mechanism of lipid enhancement of α1-adrenoceptor pressor sensitivity in hypertension

OBJECTIVE AND DESIGN

Plasma lipids enhance alpha1-adrenoceptor pressor sensitivity, impair baroreflex function, and correlate with increased blood pressure. This clinical study was designed to determine whether the enhanced alpha1-pressor sensitivity induced by acute hyperlipidemia is primarily mediated by increased vascular alpha1 responsiveness, reduced baroreflex sensitivity (BRS) or both.

METHOD

Regional alpha1-adrenoceptor vasoreactivity was measured using a graded brachial artery infusion of the alpha1 agonist, phenylephrine, in seven subjects with stage 1 hypertension. Forearm blood flow was estimated from venous occlusion plethysmography. The phenylephrine dose-forearm blood flow response curve was used to determine alpha1-vascular reactivity (slope of the dose-response curve) and sensitivity, EC50 (phenylephrine dose inducing 50% maximal response). BRS (ms/mmHg) was measured as the slope of the progressive rise in systolic blood pressure and the resultant lengthening in the subsequent R-R interval after systemic intravenous boluses of phenylephrine. Subsequently, plasma lipids were raised with a 1-h systemic co-infusion of intralipid and heparin, after which measurements of regional vasoreactivity and BRS were repeated.

RESULTS

Mean arterial pressure was 109 +/- 4 versus 110 +/- 3 (P = NS), vasoreactivity was -0.71 +/- 0.10 versus -0.82 +/- 0.10 (P = NS) and log EC50 was 1.47 +/- 0.29 versus 1.52 +/- 0.34 nmol/l (P = NS) before and after raising non-esterified fatty acids, respectively. In contrast, mean BRS was acutely reduced from 8.2 +/- 2.1 to 6.2 +/- 1.8 ms/mmHg (P = 0.02) after the lipid infusion.

CONCLUSIONS

These findings suggest that in hypertensive patients, the primary mechanism for short-term alpha1-pressor hypersensitivity in response to hyperlipidemia is via the acute impairment of BRS.

Mechanism of Fatty Acids Induced Suppression of Cardiovascular Reflexes in Rats

A blunted baroreflex sensitivity (BRS), impaired heart rate variability (HRV), and high plasma nonesterified fatty acids (NEFA) are predictors of adverse cardiovascular outcomes. We tested the hypothesis that elevation of NEFA negatively impacts the cardiac baroreflex response and undertook spectral analyses and molecular studies to delineate the mechanism of action. We used two interventions to elevate serum NEFA: 1) overnight fasting (n = 7) and 2) i.v. infusion of 1.2 ml/kg intralipid 20% + heparin (I/H) over 10 min (n = 9) in conscious unrestrained male rats. Elevated NEFA caused by fasting complemented by I/H infusion were associated with a concentration-dependent reduction in spontaneous BRS measured by spectral analysis [low-frequency alpha and high-frequency alpha (HFalpha) indices] and sequence method and HRV measured by frequency domain as power of RR interval (RRI) spectra (low-frequency RRI and high-frequency RRI) and by time domain as standard deviation of beat-to-beat interval and root mean square of successive differences along with increase in blood pressure variability measured as standard deviation of mean arterial pressure and power of systolic arterial pressure spectra (low-frequency systolic arterial pressure). Because elevated NEFA suppressed the vagal component of the baroreflex response (HFalpha), we tested the hypothesis that NEFA-evoked sequestration of myocardial muscarinic receptor (M2-mAChR) contributes to the reduced BRS. High NEFA level was accompanied by increased caveolar sequestration of cardiac M2-mAChRs without changing M2-mAChR protein expression. We report the first detailed analyses of NEFA's effect on the cardiac baroreflex and show that increased caveolar sequestration of cardiac M2-mAChRs constitutes a cellular mechanism for elevated NEFA-related deleterious cardiovascular outcomes.

Single nucleotide polymorphisms in the apolipoprotein B and low density lipoprotein receptor genes affect response to antihypertensive treatment

BACKGROUND

Dyslipidemia has been associated with hypertension. The present study explored if polymorphisms in genes encoding proteins in lipid metabolism could be used as predictors for the individual response to antihypertensive treatment.

METHODS

Ten single nucleotide polymorphisms (SNP) in genes related to lipid metabolism were analysed by a microarray based minisequencing system in DNA samples from ninety-seven hypertensive subjects randomised to treatment with either 150 mg of the angiotensin II type 1 receptor blocker irbesartan or 50 mg of the beta1-adrenergic receptor blocker atenolol for twelve weeks.

RESULTS

The reduction in blood pressure was similar in both treatment groups. The SNP C711T in the apolipoprotein B gene was associated with the blood pressure response to irbesartan with an average reduction of 19 mmHg in the individuals carrying the C-allele, but not to atenolol. The C16730T polymorphism in the low density lipoprotein receptor gene predicted the change in systolic blood pressure in the atenolol group with an average reduction of 14 mmHg in the individuals carrying the C-allele.

CONCLUSIONS

Polymorphisms in genes encoding proteins in the lipid metabolism are associated with the response to antihypertensive treatment in a drug specific pattern. These results highlight the potential use of pharmacogenetics as a guide for individualised antihypertensive treatment, and also the role of lipids in blood pressure control.

Glycine intake decreases plasma free fatty acids, adipose cell size, and blood pressure in sucrose-fed rats

The study investigated the mechanism by which glycine protects against increased circulating nonesterified fatty acids (NEFA), fat cell size, intra-abdominal fat accumulation, and blood pressure (BP) induced in male Wistar rats by sucrose ingestion. The addition of 1% glycine to the drinking water containing 30% sucrose, for 4 wk, markedly reduced high BP in sucrose-fed rats (SFR) (122.3 +/- 5.6 vs. 147.6 +/- 5.4 mmHg in SFR without glycine, P < 0.001). Decreases in plasma triglyceride (TG) levels (0.9 +/- 0.3 vs. 1.4 +/- 0.3 mM, P < 0.001), intra-abdominal fat (6.8 +/- 2.16 vs. 14.8 +/- 4.0 g, P < 0.01), and adipose cell size were observed in SFR treated with glycine compared with SFR without treatment. Total NEFA concentration in the plasma of SFR was significantly decreased by glycine intake (0.64 +/- 0.08 vs. 1.11 +/- 0.09 mM in SFR without glycine, P < 0.001). In control animals, glycine decreased glucose, TGs, and total NEFA but without reaching significance. In SFR treated with glycine, mitochondrial respiration, as an indicator of the rate of fat oxidation, showed an increase in the state IV oxidation rate of the beta-oxidation substrates octanoic acid and palmitoyl carnitine. This suggests an enhancement of hepatic fatty acid metabolism, i.e., in their transport, activation, or beta-oxidation. These findings imply that the protection by glycine against elevated BP might be attributed to its effect in increasing fatty acid oxidation, reducing intra-abdominal fat accumulation and circulating NEFA, which have been proposed as links between obesity and hypertension.

A shift in myocardial substrate, improved endothelial function, and diminished sympathetic activity may contribute to the anti-anginal impact of very-low-fat diets

A new category of anti-anginal drug - exemplified by ranolazine - is believed to work by partially inhibiting cardiac oxidation of fatty acids; oxidation of glucose requires less oxygen per mol of ATP generated, and thus is preferable to fat oxidation when oxygen availability is limiting in underperfused cardiac tissue. Unfortunately, there is no reason to believe that these drugs inhibit fat oxidation selectively in the heart; thus, chronic use of these drugs can be expected to increase body fat stores until the original rate of fat oxidation is restored by mass action - presumably negating the therapeutic benefit in angina, while exacerbating the manifold adverse effects of insulin resistance syndrome. The rational way to decrease cardiac metabolic reliance on fatty acids is to consume a very-low-fat quasi-vegan diet (i.e., 10% fat calories). Indeed, such diets are known to have a rapid and substantial therapeutic impact on anginal symptoms, while concurrently benefiting insulin sensitivity, markedly improving serum lipid profile, promoting leanness, and lessening coronary risk. A reduction in diurnal insulin secretion might also be achieved, which would be expected to decrease sympathetic activity. While reduced myocardial demand for oxygen doubtless contributes to the beneficial impact of such diets on angina, it is likely that improved cardiac perfusion consequent to improved endothelium-dependent vasodilation also plays a role in this regard. Supplemental carnitine, also beneficial in angina, appears to improve utilization of glucose in the ischemic myocardium by lowering elevated acetyl-coA levels and thereby disinhibiting pyruvate dehydrogenase. Certain other nutraceuticals may aid control of angina by improving endothelial function. In the longer term, these measures have the potential to slow or reverse the progression of stenotic lesions that underlie most cases of angina. These safe and relatively inexpensive nutritional strategies for coping with angina deserve far more attention than orthodox medical practice has thus far accorded them.

Insulin resistance and the sympathetic nervous system

The obesity epidemic is driving metabolic (insulin resistance) syndrome-related health problems including an approximately threefold increased coronary heart disease risk. Sympathetic hyperfunction may participate in the pathogenesis and complications of the metabolic syndrome including higher blood pressure, a more active renin-angiotensin system, insulin resistance, faster heart rates, and excess cardiovascular disease including sudden death. Possible factors augmenting sympathetic activation in the metabolic syndrome include alterations of insulin, leptin, nonesterified fatty acids (NEFAs), cytokines, tri-iodothyronine, eicosanoids, sleep apnea, nitric oxide, endorphins, and neuropeptide Y. Of note, high plasma NEFAs are a risk factor for hypertension and sudden death. In short-term human studies, NEFAs can raise blood pressure, heart rate, and a(1)-adrenoceptor vasoreactivity, while reducing baroreflex sensitivity, endothelium-dependent vasodilatation, and vascular compliance. Efforts to further identify the mechanisms and consequences of sympathetic dysfunction in the metabolic syndrome may provide insights for therapeutic advances to ameliorate the excess cardiovascular risk and adverse outcomes.

Moderate sodium restriction enhances the pressor response to hyperlipidemia in obese, hypertensive patients

The effect of dietary sodium restriction on insulin, lipids, and blood pressure has been controversial. Evidence suggests that adverse short-term effects in response to very low-salt diets do not persist long-term with modest sodium restriction. In this study, the effects of modest dietary sodium restriction (60 and 120 mmol sodium) were measured for 3 weeks in 12 lean normotensives and 10 obese hypertensives. Blood pressure, plasma lipids, and the pressor response to an infusion of Intralipid and heparin were obtained. In contrast to previous reports concerning very low-salt diets, obese hypertensives did not manifest a pressor response or an adverse lipid effect with moderate salt restriction. Obese hypertensives were not more salt-sensitive than lean normotensives and did not manifest a different hemodynamic response to 4-hour infusion of Intralipid and heparin while on the 120-mmol/day salt diet. During the 60-mmol/day salt diet, however, plasma triglycerides increased more in obese than in lean volunteers during the Intralipid and heparin infusion (398+/-38 vs. 264+/-18 mg/dL; p<0.05), and there were greater increases in mean blood pressure (12+/-2 vs. 7+/-2 mm Hg; p<0.05) and systemic vascular resistance (111+/-38 vs. 225+/-44 dyne.sec.cm-5) as well as a larger decrease in small artery compliance (22.5+/-0.6 vs. 20.4+/-0.6 mL/mm Hg x 100; p<0.05). These data suggest that modest dietary sodium restriction in obese hypertensives does not adversely affect baseline blood pressure or lipids, but it does magnify their adverse lipid and hemodynamic response to fat loading.

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.

New developments in mechanisms of obesity-induced hypertension: role of adipose tissue

Hypertension develops in almost 60% of obese individuals. Apart from the recent observation of obesity-associated structural changes in kidney structure that may lead to enhanced tubular sodium reabsorbtion, reports of paracrine and hormonal factors derived from adipose tissue have prompted speculations about the role of adipose tissue in the pathophysiology of obesity-induced hypertension. We summarize recent data on leptin's sympathoexcitatory actions, the possible influence of adipose tissue on atrial natriuretic peptide levels, and the formation of vasoactive substances, such as angiotensin II and nonesterified fatty acids, by adipocytes. The mechanisms discussed herein may contribute to the typical findings in obesity-induced hypertension, including volume expansion, sodium retention, enhanced sympathetic nervous system activity, increased activity of the systemic renin-angiotensin system, low atrial natriuretic peptide levels, and disturbed glucose and insulin metabolism. Together, these data strengthen the hypothesis that adipose tissue is potentially a major regulator of cardiovascular-renal function.

Nonesterified fatty acids in blood pressure control and cardiovascular complications

The fact that cardiovascular risk factors cluster among individuals with the insulin resistance syndrome strongly suggests a common pathogenetic denominator. For many years, abnormalities of nonesterified fatty acid metabolism have been implicated in the disturbances of carbohydrate and lipid metabolism that characterize the cluster. However, until more recently, evidence implicating fatty acids in the hemodynamic and vascular abnormalities that affect patients with this syndrome was lacking. Observations from epidemiological, clinical, and basic science suggest that fatty acids can raise blood pressure and contribute to the development of hypertension. The effects of fatty acids on blood pressure may be mediated in part by inhibition of endothelial nitric oxide synthase activity and endothelium-dependent vasodilation. Fatty acids can also increase alpha1-adrenoceptor-mediated vascular reactivity and induce vascular smooth muscle migration and proliferation. The adverse effects of fatty acids appear to be mediated in part through induction of oxidative stress. Fatty acids interact with other components of the risk factor cluster, including increased angiotensin II, to synergistically augment oxidative stress in cultured vascular smooth muscle cells. Oxidative stress is implicated in the pathogenesis of insulin resistance, hypertension, vascular remodeling, and vascular complications. A clearer definition of the specific reactive oxygen signaling pathways involved and interventions aimed at altering these pathways could lead to more rationale antioxidant therapy and improved outcomes.

Elevated plasma fatty acid concentrations stimulate the cardiac autonomic nervous system in healthy subjects

BACKGROUND

Fatty acids have been shown to stimulate the sympathetic nervous system in rats. Power spectral analysis of heart rate variability (HRV) is a safe and useful tool with which to evaluate cardiac autonomic nervous system (ANS) activity. Whether changes in plasma fatty acid concentrations affect the sympathetic nervous system or HRV in humans is unknown.

OBJECTIVE

We investigated the possible changes in HRV after a significant increase in plasma fatty acid concentration.

DESIGN

Subjects were randomly assigned to receive an infusion of lipid emulsion (10% triacylglycerol emulsion for 180 min) + heparin (a bolus of 200 U followed by 0.2 U*min(-)(1)*kg body wt(-)(1); n = 20) or 0.9% NaCl (for 180 min; n = 10).

RESULTS

Lipid emulsion + heparin infusion was associated with a rise in plasma epinephrine and norepinephrine concentrations. The rise in plasma fatty acid concentration was associated with a significant decline in the RR interval (P: < 0.03) and in total power (P: < 0.03). Analysis of the different components of HRV showed that lipid emulsion + heparin infusion stimulated low- frequency (LF) components (P: < 0.03 at the second hour and P: < 0. 01 at the third hour) and inhibited high-frequency (HF) components (P: < 0.03 at the second and third hours). Consequently, the LF-HF ratio was significantly stimulated (P: < 0.03 at the second hour and P: < 0.01 at the third hour). Such results persisted, although attenuated, when the study was repeated in association with a propranolol infusion (n = 8).

CONCLUSION

Elevated plasma fatty acid concentrations may stimulate cardiac autonomic nervous system activity.

Metabolic complications of obesity. Pathophysiologic considerations

Given a specific research interest in human fatty acid metabolism, this article focuses primarily on the evidence surrounding the hypothesis that dysregulation of the fuel release function of fat cells (lipolysis) is an important contributing factor to the health hazards of obesity.

Vascular effects of non-esterified fatty acids: implications for the cardiovascular risk factor cluster

Insulin resistance emerges as a central component of the risk factor cluster and is a likely contributor to vascular disease independently of traditional risk factors such as hypertension and diabetes mellitus. However, the intermediary mechanisms by which atherosclerosis is accelerated among patients with the insulin resistance syndrome remain inadequately defined. Most of the attention has centered on hyperinsulinemia and defects of insulin-mediated glucose disposal. However, we observed that obese hypertensive patients have elevated plasma concentrations of non-esterified fatty acids (NEFAs), including oleic acid, which are highly resistant to suppression by insulin. Resistance to insulin's fatty acid lowering action correlate with blood pressure in obese subjects independently of defects in glucose disposal. This observation raises the possibility that NEFAs have biologically significant effects on the cardiovascular system. In fact, oleic acid impairs nitric oxide synthase activity and endothelium-dependent vasorelaxation in vitro. Moreover, raising NEFAs in normal human volunteers to levels observed in obese hypertensive patients impairs lower extremity endothelium-dependent vasodilation and augments local and systemic vascular alpha1-adrenoceptor reactivity in normal volunteers. Thus, raising NEFAs replicates in healthy subjects important functional vascular changes implicated in the hypertension and atherosclerosis observed in patients with the risk factor cluster. At a molecular level, experiments in cultured vascular smooth muscle cells demonstrate that oleic acid activates a mitogenic signaling cascade which includes protein kinase C, reactive oxygen species and extracellular signal-regulated kinases. Each of these signaling events has been implicated in the structural and functional vascular changes which accompany the risk factor cluster. Collectively, these observations raise the possibility that fatty acids contribute to functional and structural vascular changes among insulin-resistant individuals. A better understanding of the signaling mechanisms by which NEFAs exert their vascular effects may facilitate novel and more effective therapeutic approaches to managing the cardiovascular risk factor cluster.