Differential blood pressure effects of oral glucose and intravenous L-arginine in healthy lean normotensive and obese hypertensive subjects

l-Arginine inhibits the activity of α-amylase: Rapid kinetics, interaction and functional implications

In this work, the rapid unfolding kinetics of pancreas α-amylase (PPA) induced by l-arginine and the interaction mechanism were investigated. The unfolding followed a first-level reaction kinetics equation, without intermediates. l-arginine interacted with PPA though diffusion-controlled process rather than complexion. The interaction between l-arginine and PPA resulted in a pronounced decrease in β-sheet and a significant increase in random coil, and thereby the enzyme activity decreased. However, the unfolding of PPA could be compensated and the second structure change could be recovered to some extent by the macromolecular crowded medium of Pluronics. Further insight into the mechanism disclosed that the broken H-bond network of water may contribute to PPA unfolding. This work provides a new perspective on the interaction of l-arginine with digestive enzyme. The unfolding mechanism of enzymes by may help to understand the effects of other structurally similar drugs, which is of concern in food-drug interactions.

Amino Acids in Circulatory Function and Health

Cardiovascular disease is the major cause of global mortality and disability. Abundant evidence indicates that amino acids play a fundamental role in cardiovascular physiology and pathology. Decades of research established the importance of L-arginine in promoting vascular health through the generation of the gas nitric oxide. More recently, L-glutamine, L-tryptophan, and L-cysteine have also been shown to modulate vascular function via the formation of a myriad of metabolites, including a number of gases (ammonia, carbon monoxide, hydrogen sulfide, and sulfur dioxide). These amino acids and their metabolites preserve vascular homeostasis by regulating critical cellular processes including proliferation, migration, differentiation, apoptosis, contractility, and senescence. Furthermore, they exert potent anti-inflammatory and antioxidant effects in the circulation, and block the accumulation of lipids within the arterial wall. They also mitigate known risk factors for cardiovascular disease, including hypertension, hyperlipidemia, obesity, and diabetes. However, in some instances, the metabolism of these amino acids through discrete pathways yields compounds that fosters vascular disease. While supplementation with amino acid monotherapy targeting the deficiency has ameliorated arterial disease in many animal models, this approach has been less successful in the clinic. A more robust approach combining amino acid supplementation with antioxidants, anti-inflammatory agents, and/or specific amino acid enzymatic pathway inhibitors may prove more successful. Alternatively, supplementation with amino acid-derived metabolites rather than the parent molecule may elicit beneficial effects while bypassing potentially harmful pathways of metabolism. Finally, there is an emerging recognition that circulating levels of multiple amino acids are perturbed in vascular disease and that a more holistic approach that targets all these amino acid derangements is required to restore circulatory function in diseased blood vessels.

Arginine impairs endothelial and executive function in older subjects with cardiovascular risk

Neurovascular coupling, the relationship between cerebral blood flow and neuronal activity, is attenuated in patients with impaired executive function. We tested the hypothesis that peripheral vascular function may associate with executive function in older subjects with cardiovascular risk factors and that treatment with the antioxidant L-arginine would improve both vascular and executive function. Nineteen subjects with type 2 diabetes mellitus and/or controlled hypertension were enrolled. Subjects were treated with L-arginine or placebo for 4 days in a randomized, double-blinded, cross-over study. Brachial artery vascular function, peripheral artery tonometry, and Trail Making Test Part B testing were performed on day 1 and day 4 during each condition. L-arginine significantly reduced the digital reactive hyperemia index, and the comparison of changes against placebo was significant (P = .01). With executive function testing, we observed a significant interaction between treatment and order. Restricting the analysis to the first treatment period, subjects treated with placebo decreased their Trail Making Test Part B times by 57.3 ± 52.5 seconds from day 1 to day 4 (P = .01) while those treated with arginine had no significant change (6.4 ± 18.4 seconds worse, P = .37). In addition, L-arginine was associated with increased mean arterial pressure from 88 ± 9 mm Hg to 92 ± 11 mm Hg, which trended toward significance. L-arginine treatment worsened digital microvascular and executive function in older subjects with cardiovascular risk factors. These data further support a link between vascular and executive function.

Arginase promotes endothelial dysfunction and hypertension in obese rats

OBJECTIVE

This study investigated whether arginase contributes to endothelial dysfunction and hypertension in obese rats.

METHODS

Endothelial function and arginase expression were examined in skeletal muscle arterioles from lean and obese Zucker rats (ZRs). Arginase activity, arginine bioavailability, and blood pressure were measured in lean and obese animals.

RESULTS

Arginase activity and expression was increased while global arginine bioavailability decreased in obese ZRs. Acetylcholine or luminal flow caused dilation of isolated skeletal muscle arterioles, but this was reduced or absent in vessels from obese ZRs. Treatment of arterioles with a nitric oxide synthase inhibitor blocked dilation in lean arterioles and eliminated differences among lean and obese vessels. In contrast, arginase inhibitors or l-arginine enhanced vasodilation in obese ZRs and abolished differences between lean and obese animals, while d-arginine had no effect. Finally, mean arterial blood pressure was significantly increased in obese ZRs. However, administration of l-arginine or arginase inhibitors lowered blood pressure in obese but not lean animals, and this was associated with an improvement in systemic arginine bioavailability.

CONCLUSIONS

Arginase promotes endothelial dysfunction and hypertension in obesity by reducing arginine bioavailability. Therapeutic approaches targeting arginase represent a promising approach in treating obesity-related vascular disease.

Effects of pharmaconutrients on cellular dysfunction and the microcirculation in critical illness

PURPOSE OF REVIEW

A growing body of data has revealed that specific nutrient deficiencies contribute to microvascular and cellular dysfunction following critical illness. Further, targeted administration of these 'pharmaconutrients' may reverse or improve this dysfunction and improve clinical outcome.

RECENT FINDINGS

Specific nutrient therapy with glutamine protects cellular metabolism and vascular function via induction of heat shock proteins, which are key proteins found to be deficient following acute illness. Arginine becomes rapidly deficient following trauma and surgery. This leads to significant immunosuppression, which when treated by arginine administration significantly reduces postoperative infection. Omega-3 fatty acids attenuate the inflammatory response and provide for resolution of ongoing inflammatory injury via production of resolvins/protectins. Antioxidants (vitamin C and selenium) and trace elements (zinc) become rapidly depleted in critical illness and replacement appears vital to ensure optimal cellular and microvascular function. Data on targeted metabolic (mitochondrial) therapies (i.e. co-enzyme Q10) show promise to improve myocardial function following cardiac surgery.

SUMMARY

These specific nutrients have newly discovered vital mechanistic roles in the optimization of cellular and microcirculatory function in critical illness and injury. A growing body of literature is demonstrating that correction of key nutrient deficiencies via therapeutic administration of these pharmaconutrients can improve clinical outcome in critically ill patients.

Exogenous arginine in sepsis

Sepsis is a severe condition in critically ill patients and is considered an arginine deficiency state. The rationale for arginine deficiency in sepsis is mainly based on the reduced arginine levels in sepsis that are associated with the specific changes in arginine metabolism related to endothelial dysfunction, severe catabolism, and worse outcome. Exogenous arginine supplementation in sepsis shows controversial results with only limited data in humans and variable results in animal models of sepsis. Since in these studies the severity of sepsis varies but also the route, timing, and dose of arginine, it is difficult to draw a definitive conclusion for sepsis in general without considering the influence of these factors. Enhanced nitric oxide production in sepsis is related to suggested detrimental effects on hemodynamic instability and enhanced oxidative stress. Potential mechanisms for beneficial effects of exogenous arginine in sepsis include enhanced (protein) metabolism, improved microcirculation and organ function, effects on immune function and antibacterial effects, improved gut function, and an antioxidant role of arginine. We recently performed a study indicating that arginine can be given to septic patients without major effects on hemodynamics, suggesting that more studies can be conducted on the effects of arginine supplementation in septic patients.

Preclinical trial of L-arginine monotherapy alone or with N-acetylcysteine in septic shock

OBJECTIVE

L-arginine supplementation in sepsis is controversial. Septic shock has been alternatively viewed as an L-arginine-deficient state or as a syndrome caused by excess nitric oxide, an end-product of L-arginine metabolism.

DESIGN

Randomized, placebo-controlled, and double-blinded (investigators, veterinarians, and pharmacists).

SETTING

Laboratory.

SUBJECTS

Purpose-bred, 1- to 2-yr-old, 10- to 12-kg beagles.

INTERVENTIONS

The effects of parenteral L-arginine alone or in combination with N-acetylcysteine were compared with vehicle alone in a well-characterized canine model of Escherichia coli peritonitis. Two doses were studied that delivered approximately 1.5-fold (10 mg x kg(-1) x hr(-1)) and 15-fold (100 mg x kg(-1) x hr(-1)) the L-arginine dose typically administered with standard total parenteral nutrition. Animals in the low- and high-dose L-arginine arms were further randomized to receive vehicle alone or N-acetylcysteine (20 mg x kg(-1) x hr(-1)) as an antioxidant to prevent peroxynitrite formation.

MEASUREMENTS AND MAIN RESULTS

The main measurements were hemodynamics, plasma arginine and ornithine, serum nitrate/nitrite, laboratory studies for organ injury, and survival. Both doses of L-arginine similarly increased mortality (p = .02), and worsened shock (p = .001 for reduced mean arterial pressure). These effects were associated with significant increases in plasma arginine (p = .0013) and ornithine (p = .0021). In addition, serum nitrate/nitrite (p = .02), liver enzymes (p = .08), and blood urea nitrogen/creatinine ratios (p = .001) rose, whereas arterial pH (p = .001) and bicarbonate levels (p = .001) fell. N-acetylcysteine did not significantly decrease any of the harmful effects of L-arginine. Thus, parenteral L-arginine monotherapy was markedly harmful in animals with septic shock.

CONCLUSIONS

These findings suggest that supplemental parenteral L-arginine, at doses above standard dietary practices, should be avoided in critically ill patients with septic shock.