Glutamate transport asymmetry and metabolism in the functioning kidney

Metabolomics and psychological features in fibromyalgia and electromagnetic sensitivity

Fibromyalgia (FM) as Fibromyalgia and Electromagnetic Sensitivity (IEI-EMF) are a chronic and systemic syndrome. The main symptom is represented by strong and widespread pain in the musculoskeletal system. The exact causes that lead to the development of FM and IEI-EMF are still unknown. Interestingly, the proximity to electrical and electromagnetic devices seems to trigger and/or amplify the symptoms. We investigated the blood plasma metabolome in IEI-EMF and healthy subjects using ¹H NMR spectroscopy coupled with multivariate statistical analysis. All the individuals were subjected to tests for the evaluation of psychological and physical features. No significant differences between IEI-EMF and controls relative to personality aspects, Locus of Control, and anxiety were found. Multivariate statistical analysis on the metabolites identified by NMR analysis allowed the identification of a distinct metabolic profile between IEI-EMF and healthy subjects. IEI-EMF were characterized by higher levels of glycine and pyroglutamate, and lower levels of 2-hydroxyisocaproate, choline, glutamine, and isoleucine compared to healthy subjects. These metabolites are involved in several metabolic pathways mainly related to oxidative stress defense, pain mechanisms, and muscle metabolism. The results here obtained highlight possible physiopathological mechanisms in IEI-EMF patients to be better defined.

d-Amino Acid Peptide Residualizing Agents for Protein Radioiodination: Effect of Aspartate for Glutamate Substitution

The residualizing prosthetic agent N^ε-(3-[^*I]iodobenzoyl)-Lys⁵-N^α-maleimido-Gly¹-d-GEEEK ([^*I]IB-Mal-d-GEEEK) showed promise for the radioiodination of monoclonal antibodies (mAbs) that bind to internalizing molecular targets. Although enhanced tumor uptake was achieved in these studies, elevated kidney accumulation also was observed, particularly with low-molecular-weight, single-domain antibody fragments (sdAbs). Here, we developed an analogous agent (IB-Mal-d-GDDDK), in which glutamate residues (E) were replaced with aspartates (D) to determine whether this modification could decrease renal uptake. [¹²⁵I]IB-Mal-d-GDDDK and [¹³¹I]IB-Mal-d-GEEEK were synthesized with similar radiochemical yields (60–80%) and coupled to the anti-HER2 sdAb 5F7 at 50–60% efficiency. Paired-label internalization assays in vitro indicated similar levels of intracellular activity residualization in HER2-expressing BT474M1 cells for [¹²⁵I]IB-Mal-d-GDDDK-5F7 and [¹³¹I]IB-Mal-d-GEEEK-5F7. A paired-label biodistribution comparison of the two labeled conjugates was performed in mice with HER2-expressing SKOV-3 xenografts, and the results of this study indicated that renal uptake at 1 h was 127.5 ± 18.7% ID/g and 271.4 ± 66.6% ID/g for [¹²⁵I]IB-Mal-d-GDDDK-5F7 and [¹³¹I]IB-Mal-d-GEEEK-5F7, respectively. The tumor uptake of the two radioconjugates was not significantly different. These results demonstrate that substitution of E with D in the IB-Mal-d-GEEEK construct reduced kidney accumulation of the sdAb. However, renal activity levels need to be reduced further if d-amino acid derived prosthetic agents are to be of practical value for labeling low molecular weight biomolecules such as sdAbs.

Emerging Roles of Branched-Chain Amino Acid Supplementation in Human Diseases

The branched-chain amino acids (BCAAs), namely, valine, leucine, and isoleucine, are indispensable amino acids required for body protein synthesis. Unlike other amino acids, the BCAAs are primarily catabolised in the extrahepatic tissues. The BCAAs play role in regulation of protein synthesis and turnover as well as maintenance of the body glutamate-glutamine level. In strenuous and traumatic conditions, the BCAAs are oxidized which limits their availability in tissues. Such condition affects the body glutamate-glutamine pool and protein synthesis mechanisms. Thus BCCA supplementation is emerging as a nutritional strategy for treating many diseases. Many studies have found that BCAA administration is able to improve the health status of the patients suffering from different diseases even though there are conditions where they do not exert any effect. There are also some reports where elevated BCAAs have been shown to be associated with the pathogenesis of diseases. In this review, we have discussed the implication of BCAA supplementation in different pathological conditions and their relevant outcomes.

Improved tumor targeting of anti-HER2 nanobody through N-succinimidyl 4-guanidinomethyl-3-iodobenzoate radiolabeling

Nanobodies are approximately 15-kDa proteins based on the smallest functional fragments of naturally occurring heavy chain-only antibodies and represent an attractive platform for the development of molecularly targeted agents for cancer diagnosis and therapy. Because the human epidermal growth factor receptor type 2 (HER2) is overexpressed in breast and ovarian carcinoma, as well as in other malignancies, HER2-specific Nanobodies may be valuable radiodiagnostics and therapeutics for these diseases. The aim of the present study was to evaluate the tumor-targeting potential of anti-HER2 5F7GGC Nanobody after radioiodination with the residualizing agent N-succinimidyl 4-guanidinomethyl 3-(125/131)I-iodobenzoate (*I-SGMIB).

METHODS

The 5F7GGC Nanobody was radiolabeled using *I-SGMIB and, for comparison, with N(ε)-(3-*I-iodobenzoyl)-Lys(5)-N(α)-maleimido-Gly(1)-GEEEK (*I-IB-Mal-d-GEEEK), another residualizing agent, and by direct radioiodination using IODO-GEN ((125)I-Nanobody). The 3 labeled Nanobodies were evaluated in affinity measurements, and paired-label internalization assays were performed on HER2-expressing BT474M1 breast carcinoma cells and in paired-label tissue distribution measurements in mice bearing subcutaneous BT474M1 xenografts.

RESULTS

*I-SGMIB-Nanobody was produced in 50.4% ± 3.6% radiochemical yield and exhibited a dissociation constant of 1.5 ± 0.5 nM. Internalization assays demonstrated that intracellular retention of radioactivity was up to 1.5-fold higher for *I-SGMIB-Nanobody than for coincubated (125)I-Nanobody or *I-IB-Mal-d-GEEEK-Nanobody. Peak tumor uptake for *I-SGMIB-Nanobody was 24.50% ± 9.89% injected dose/g at 2 h, 2- to 4-fold higher than observed with other labeling methods, and was reduced by 90% with trastuzumab blocking, confirming the HER2 specificity of localization. Moreover, normal-organ clearance was fastest for *I-SGMIB-Nanobody, such that tumor-to-normal-organ ratios greater than 50:1 were reached by 24 h in all tissues except lungs and kidneys, for which the values were 10.4 ± 4.5 and 5.2 ± 1.5, respectively.

CONCLUSION

Labeling anti-HER2 Nanobody 5F7GGC with *I-SGMIB yields a promising new conjugate for targeting HER2-expressing malignancies. Further research is needed to determine the potential utility of *I-SGMIB-5F7GGC labeled with (124)I, (123)I, and (131)I for PET and SPECT imaging and for targeted radiotherapy, respectively.

Aortic leucine-to-glutamate pathway: metabolic route and regulation of contractile responses

Rat aortic endothelium is differentiated regionally for three signal pathways capable of regulating the cGMP content of the underlying smooth muscle. Formation of nitric oxide (NO) from L-arginine and of glutamate from L-leucine increase cGMP; however, formation of prostaglandin H2 (PGH2) decreases cGMP. All three have peak activity in the windkessel area just distal to the aortic arch and decrease peripherally. We report evidence that the biochemical route of the leucine-to-glutamate (Leu-->Glu) pathway is via metabolism of leucine to acetyl CoA, that the controlling reaction of the pathway is mediated by the branched chain alpha-ketoacid dehydrogenase complex (BCDC), and that glutamate formation via the Leu-->Glu pathway is a major source of aortic segment free glutamate in vitro. Interruption of the pathway by treatment of precontracted rat aortic rings in vitro with each of three classes of inhibitors (leucine analogs, competitors for the BCDC reaction, or inhibitors of L-glutamate transport) enhances contractile responses. The enhancement requires an intact endothelium and is not owing to reductions in NO formation. The results support the hypothesis that the Leu-->Glu pathway functions in the regulation of aortic contractility and compliance.

Regulatory responses to an oral D-glutamate load: formation of D-pyrrolidone carboxylic acid in humans

Previously published studies have shown D-glutamate to be the most potent natural inhibitor of glutathione synthesis known, yet how D-glutamate is handled in humans is unknown. Therefore, we administered an oral D-glutamate load to four healthy volunteers and monitored the plasma D-glutamate concentration and excretion over a 3-h postload period. Compared with time controls, the plasma D-glutamate concentration increased 10-fold in the 1st h and then reached a plateau over the remaining time course. In contrast, plasma D-pyrrolidone carboxylic acid increased progressively throughout the 3-h time course to a level 10-fold higher than the D-glutamate plasma concentration. Excretion of D-glutamate progressively increased despite a constant filtered D-glutamate load rising from only 5 to 95% of the filtered amount. Excretion of D-pyrrolidone carboxylic acid increased with the rise in filtered load without significant reabsorption. The amount of D-pyrrolidone carboxylic acid excreted over the 3-h time course was 10 times the amount excreted as D-glutamate and accounted for almost 20% of the administered D-glutamate. These findings indicate that plasma D-glutamate concentration is tightly regulated through two mechanisms: 1) the transport into cells and metabolic conversion to D-pyrrolidone carboxylic acid and excretion, and 2) the enhancement of D-glutamate clearance by the kidneys.