Naji Abumrad

Reversal of cancer-related wasting using oral supplementation with a combination of β-hydroxy-β-methylbutyrate, arginine, and glutamine

Background: Cancer-related cachexia is caused by a diverse combination of accelerated protein breakdown and slowed protein synthesis. The hypothesis proposed in this study is that supplementation of specific nutrients known to positively support protein synthesis and reduce protein breakdown will reverse the cachexia process in advanced cancer patients. Methods: Patients with solid tumors who had demonstrated a weight loss of at least 5% were considered for the study. Patients were randomly assigned in a double-blind fashion to either an isonitrogenous control mixture of nonessential amino acids or an experimental treatment containing -hydroxy--methylbutyrate (3 g/d), L-arginine (14 g/d), and L-glutamine (14 g/d [HMB/Arg/Gln]). The primary outcomes measured were the change in body mass and fat-free mass (FFM), which were assessed at 0, 4, 8, 12, 16, 20, and 24 weeks. Results: Thirty-two patients (14 control, 18 HMB/Arg/Gln) were evaluated at the 4-week visit. The patients supplemented with HMB/ Arg/Gln gained 0.95 0.66 kg of body mass in 4 weeks, whereas control subjects lost 0.26 0.78 kg during the same time period. This gain was the result of a significant increase in FFM in the HMB/Arg/Gln-supplemented group (1.12 0.68 kg), whereas the subjects supplemented with the control lost 1.34 0.78 kg of FFM (P 0.02). The response to 24-weeks of supplementation was evaluated by an intent-to-treat statistical analysis. The effect of HMB/Arg/Gln on FFM increase was maintained over the 24 weeks (1.60 0.98 kg; quadratic contrast over time, P 0.05). There was no negative effect of treatment on the incidence of adverse effects or quality of life measures. Conclusions: The mixture of HMB/Arg/Gln was effective in increasing FFM of advanced (stage IV) cancer. The exact reasons for this improvement will require further investigation, but could be attributed to the observed effects of HMB on slowing rates of protein breakdown, with improvements in protein synthesis observed with arginine and glutamine.

Dopamine D2 receptor availability in opiate-dependent subjects before and after naloxone-precipitated withdrawal.

Dopamine may play a role in opiate withdrawal and dependence. We measured dopamine D2 receptor availability in 11 opiate-dependent subjects using PET and [11C]raclopride at baseline and during naloxone-precipitated withdrawal. Because [11C]raclopride is sensitive to endogenous dopamine, this strategy enabled us to test whether we could document in humans the DA reductions reported in animal models of opiate withdrawal. Results were compared with values from 11 controls, two of which also received naloxone. The ratio of the distribution volume in striatum to that in cerebellum (Bmax/Kd + 1) was used as model parameter for D2 receptor availability. Baseline measures for Bmax/Kd were lower in opiate-dependent subjects (2.44 ± 0.4) than in controls (2.97 ± 0.45, p ≤. 009). Naloxone precipitated an intense withdrawal in the abusers but did not change the Bmax/Kd ratio. This study documents decreases in D2 receptors in opiate-dependent subjects but does not document significant changes in striatal DA concentration during acute withdrawal.

Nutritional role of the leucine metabolite β-hydroxy β-methylbutyrate (HMB)

This review develops the hypothesis that a metabolite of leucine termed β-hydroxy β-methylbutyrate (HMB) plays a key role in animal metabolism and that in certain circumstances insufficient amounts of HMB are either consumed in the diet or produced endogenously to supply tissue needs. The origin and metabolism of HMB is reviewed including the role of HMB in cholesterol biosynthesis. HMB feeding studies in animals are reviewed, which indicate that dietary supplementation of HMB can improve immune function and health and can increase the fat content of milk in lactating animals. Seven human studies are reviewed where HMB was fed. The results of both animal and human studies indicate that dietary supplementation of HMB is safe, as evidenced by lack of physical adverse effects and a lack of effect on blood hematology and chemistry. The only consistent change in blood chemistry was a decrease in LDL cholesterol, which changed 7% (P < .01). In humans undergoing resistance training, HMB supplementation increased lean mass gains from 50 to 200%, with similar percentage increases in strength when compared with unsupplemented subjects. The effects of HMB on muscle size and function seems to result from a diminution of exercise-related muscle damage and muscle protein breakdown. A general hypothesis is proposed that HMB is metabolized to HMG-CoA in tissues such as muscle, mammary tissue, and certain immune cells and is used for de novo cholesterol synthesis. In times of stimulated growth and/or differentiation. HMG-CoA may be rate-limiting for cholesterol synthesis, which could limit cell growth or function. It is proposed that feeding HMB can provide a saturating source of cytosolic HMG-CoA for cholesterol synthesis and in turn allow for maximal cell growth and function.

Fluoro-norchloroepibatidine: Preclinical assessment of acute toxicity

18Fluoro-norchloroepibatidine (exo-2-(6-fluoro-3-pyridyl)-7-azabicyclo-[2.2.1]heptane [NFEP]), a labeled derivative of epibatidine, has shown promise for imaging brain nicotinic acetylcholine receptors with PET. We determined the dose-dependent effects of NFEP in conscious rats. NFEP (1.5 microg/kg; administered intravenously) resulted in 30% mortality. Neither 0.5 microg/kg or 0.25 microg/kg NFEP resulted in any significant changes in cardiorespiratory parameters, but plasma catecholamines increased (2- to 3-fold). Further studies are needed to determine the safety of NFEP that are specifically designed to assess the catecholamine response. Our results suggest that it is not advisable to initiate human PET studies with [18F]-NFEP without further evidence supporting its safety.

Differential effects of hemorrhage and LPS on tissue TNF-α, IL-1 and associate neuro-hormonal and opioid alterations

LPS administration and hemorrhage are frequently used models for the in vivo study of the stress response. Both challenges stimulate cytokine production as well as activate opiate and neuro-endocrine pathways; which in turn modulate the inflammatory process. Differences in the magnitude and tissue specificity of the proinflammatory cytokine and neuro-hormonal responses to these stressors are not well established. We contrasted the tissue specificity and magnitude of the increase in circulating and tissue cytokine (TNF-alpha, IL-1alpha and IL-1beta) content in response to either fixed-pressure hemorrhage (approximately 40 mm Hg) followed by fluid resuscitation (HEM) or lipopolysaccharide (LPS; 100 microg/100 g BW) administration. LPS and HEM elevated circulating levels of TNF-alpha, while neither stress altered circulating IL-1-alpha and IL-beta. LPS-induced increases in TNF-alpha content were greater than those elicited by HEM in all tissues studied except for the lung, where both stressors produced similar increases. Tissue (lung, spleen and heart) content of IL-1alpha was increased by HEM but was not affected by LPS. Tissue (lung, spleen, and heart) content of IL-1beta was increased by LPS but was not affected by HEM. HEM produced greater increases than LPS in epinephrine (16- vs. 4-fold) and norepinephrine (4-fold vs. 60%) levels and similar elevations in beta-endorphin. LPS produced greater elevation in corticosterone levels (2-fold) than HEM (50%). These results suggest differential tissue cytokine modulation to HEM and LPS, both with respect to target tissue and cytokine type. The hormonal milieu to HEM is characterized by marked catecholaminergic and moderate glucocorticoid while that of LPS is characterized by marked glucocorticoid with moderate catecholaminergic influence.

Renal Glucose Production During Insulin-Induced Hypoglycemia

Recent in vivo studies have rekindled interest in the role of the kidney in glucose metabolism. We therefore undertook the present study to evaluate the contribution of the kidney to systemic glucose production and utilization rates during insulin-induced hypoglycemia using arteriovenous balance combined with a tracer technique. Ten days after the surgical placement of sampling catheters in the right and left renal veins and femoral artery and of an infusion catheter in the left renal artery of dogs, systemic and renal glucose kinetics were measured with the peripheral infusion of [6-3H]glucose. Renal blood flow was determined with a flowprobe. After baseline, six dogs received 2-h simultaneous infusions of peripheral insulin (4 mU · kg−1 · min−1) and left intrarenal [6,6-2H]dextrose (14 μmol · kg−1 · min−1) to achieve and maintain left renal normoglycemia during systemic hypoglycemia. Arterial glucose decreased from 5.3 ± 0.1 to 2.2 ± 0.1 mmol/1; insulin increased from 46 ± 5 to 1,050 ± 50 pmol/1; epinephrine increased from 130 ± 8 to 1,825 ± 50 pg/ml; norepinephrine increased from 129 ± 6 to 387 ± 15 pg/ml; and glucagon increased from 52 ± 2 to 156 ± 12 pg/ml (all P < 0.01). Systemic glucose appearance increased from 16.6 ± 0.4 μmol · kg−1 · min−1 in the baseline to 24.2 ± 0.6 μmol · kg−1 · min−1 during hypoglycemia when endogenous glucose production was 10.2 ± 1.0 μmol · kg−1 · min−1 (P < 0.01). In the baseline, the liver accounted for 80% (13.3 ± 0.8 μmol · kg−1 · min−1) and each kidney contributed 10% (1.6 ± 0.2 μmol · kg−1 · min−1) to endogenous glucose production. During hypoglycemia, however, hepatic glucose production decreased to 4.0 ± 0.4 μmol · kg−1 · min−1, whereas right renal glucose production doubled to 3.2 ± 0.2 μmol · kg−1 · min−1 (P < 0.01). Left renal glucose production was 17 ± 2 μmol · kg−1 · min−1, 14 of which were derived from the exogenous infusion. These results indicate that glucose production by the kidney is stimulated by counterregulatory hormones and represents an important component of the bodys defense against insulin-induced hypoglycemia.

Contribution of excitatory amino acids to hypoglycemic counter-regulation

We determined the contribution of central N-methyl-D-aspartate (NMDA) receptor activation to the neuro-endocrine counter-regulatory response to insulin-induced hypoglycemia. Glucose kinetics, gluconeogenic substrate balance and counter-regulatory hormonal responses were determined in two groups of conscious dogs fitted with chronic vascular catheters and intracerebroventricular (i.c.v.) cannula. Peripheral insulin infusion (5 mU/kg per min for 3 h) decreased plasma glucose levels 40% and increased the rate of glucose appearance (R(a)) 2-fold. This was associated with significant increases in net hepatic uptake of glycerol and lactate, without any change in the net hepatic uptake of alanine. i.c.v. pretreatment with MK-801, an NMDA receptor antagonist, blunted (50%) the rise in glucose R(a) as well as the increase in the net hepatic uptake of glycerol and lactate. Hypoglycemia increased plasma cortisol (3-fold to 14.3+/-1 mg/dl) and epinephrine levels (14-fold to 3811+/-172 pg/ml), and this stress response was attenuated (30% and 60%, respectively) by MK-801 pretreatment. In controls, MK-801 did not alter the increase in norepinephrine or glucagon elicited by hypoglycemia. These results indicate that during hypoglycemia, central excitatory amino acids contribute to the modulation of the glucoregulatory response through activation of NMDA receptors, resulting in stimulation of the sympathoadrenal and hypothalamic-pituitary adrenal axis. This mechanism appears to play an important role in the sustained elevation in hepatic glucose production during hypoglycemia.

Central sympathetic modulation of tissue cytokine response to hemorrhage.

Hemorrhage is associated with altered immune responses as well as with early increases in circulating levels and tissue content of proinflammatory cytokines. The present study determined the effects of central chemical sympathectomy on the early increase in tissue content of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) following fixed-pressure (40 mm Hg) hemorrhage as well as on the associated activation of the opiate and glucocorticoid systems. Conscious unrestrained nonheparinized male Sprague-Dawley rats were randomized to receive either 6-hydroxydopamine intracerebroventricularly or equal volumes of saline (5 µl). Half of the animals in each group underwent hemorrhage followed by fluid resuscitation with lactated Ringer’s solution, and were sacrificed at completion of the resuscitation period. Hemorrhage elevated TNF-α and IL-6 content in spleen (30–47%) and lung (∼40%). Central chemical sympathectomy did not alter tissue cytokine content or circulating levels of β-endorphin and corticosterone. However, central chemical sympathectomy attenuated the hemorrhage-induced increase in lung and spleen TNF-α, enhanced the IL-6 response in spleen and blunted the rise in circulating β-endorphin levels. These results demonstrate central modulation of the inflammatory and opiate responses to hemorrhagic stress.

Co-administration of gamma-vinyl GABA and cocaine: preclinical assessment of safety.

Gamma-vinyl GABA (GVG, Vigabatrin), an irreversible inhibitor of GABA transaminase (GABA-T) that inhibits cocaine-induced place preference and self administration has been proposed as a treatment for cocaine addiction. It was therefore important to assess if there was an enhanced toxicity from the combination of GVG with cocaine. No mortality was observed with administration of GVG (60 mg/kg i.v.) alone (n=8) or in combination (n=6) with cocaine (5 mg/kg i.v.). Cocaine-induced EKG alterations were not affected by GVG pretreatment. Plasma alanine amino transferase activity was reduced by GVG treatment and this was not further modified by cocaine administration. These results suggest that acute co-administration of GVG and cocaine does not result in immediate cardiovascular or hepatic toxicity of sufficient significance, to preclude further clinical trials.

Differential responses of brain, liver, and muscle glycogen to opiates and surgical stress

We examined the effects of intracerebroventricular (ICV) cannula implantation followed by the administration of morphine sulfate (MOR) and its metabolite, morphine-6-glucuronide (M6G), on the glycogen content of the brain, liver, and muscle. ICV cannulation resulted in nearly a 30% reduction in brain glycogen, and ICV MOR resulted in a 36% reduction in liver glycogen content compared to timematched controls, but it had no additional effect on either the brain or muscle glycogen content. ICV M6G showed a more significant reduction, to 50% of liver glycogen, but it had no effect on either brain or muscle glycogen. Neither IV MOR nor M6G produced any significant alteration in tissue glycogen content. These results indicate that the stress response associated with neurosurgery, especially the placement of the ICV cannula, is associated with a decrement in brain glycogen. The activation of opioid receptors in the brain results in enhanced hepatic glycogenolysis but has no additional effect on the brain glycogen content.