Integrated Proteomic and Metabolomic Analyses of the Mitochondrial Neurodegenerative Disease MELAS

MELAS (mitochondrial encephalomyopathy, lactic acidosis, stroke-like episodes) is a progressive neurodegenerative disease caused by pathogenic mitochondrial DNA variants. The pathogenic mechanism of MELAS remains enigmatic due to the exceptional clinical heterogeneity and the obscure genotype-phenotype correlation among MELAS patients. To gain insights into the pathogenic signature of MELAS, we designed a comprehensive strategy integrating proteomics and metabolomics in patient-derived dermal fibroblasts harboring the ultra-rare MELAS pathogenic variant m.14453G>A, specifically affecting the mitochondrial respiratory Complex I. Global proteomics was achieved by data-dependent acquisition (DDA) and verified by data-independent acquisition (DIA) using both Spectronaut and the recently launched MaxDIA platforms. Comprehensive metabolite coverage was achieved for both polar and nonpolar metabolites in both reverse phase and HILIC LC-MS/MS analyses. Our proof-of-principle MELAS study with multi-omics integration revealed OXPHOS dysregulation with a predominant deficiency of Complex I subunits, as well as alterations in key bioenergetic pathways, glycolysis, tricarboxylic acid cycle, and fatty acid β-oxidation. The most clinically relevant discovery is the downregulation of the arginine biosynthesis pathway, likely due to blocked argininosuccinate synthase, which is congruent with the MELAS cardinal symptom of stroke-like episodes and its current treatment by arginine infusion. In conclusion, we demonstrated an integrated proteomic and metabolomic strategy for patient-derived fibroblasts, which has great clinical potential to discover therapeutic targets and design personalized interventions after validation with a larger patient cohort in the future.

Intravenous isotonic fluid challenge, and L-arginine infusion for oligoamnios and diminished fetal movements: a preliminary study

Background: Utero-placental insufficiency is one of the major causes of oligoamnios and diminished fetal movements (FM). Rapid intravenous isotonic fluid infusion within the cardiovascular reserve improves tissue perfusion in all systems. We tested the hypothesis that isotonic fluid challenge may improve uteroplacental perfusion, which may, in turn improve fetal oxygenation, liquor formation, and FM.Methods: In this descriptive study, twenty-three antenatal mothers with gestational age >26 weeks, and with amniotic fluid index (AFI) <8 cm were included. Intravenous isotonic fluid challenge with 2 or 3 pints of ringer’s lactate, at the rate of 180-200 drops/minute, twice daily for 2-3days and, L-arginine infusion, 300 ml/day alternate days for 2-3 doses were given. Women were advised to take more than 3 litres of water a day. AFI was recorded once daily for 5 days, and then biweekly. The fluid challenge was repeated whenever AFI diminished <8.00 cm. AFI and perceived FM were graded. Pregnancies were terminated when there was no response to fluid challenge. The trend of changes in AFI and FM grades, number of days pregnancies continued, and perinatal outcomes were recorded.Results: We noted recurrent fall in AFI after an initial arise in 20 women, which required recurrent fluid challenges. Pregnancies could be continued for 18±8.5 days (median±SD). Three women, with case of absent FM, reported FM within 1 hour after initiation of the fluid challenge. There were no perinatal deaths.Conclusions: Intravenous isotonic fluid challenge and L-arginine infusion, improves AFI and FM, and helps to prolong pregnancies towards viability.

Oxytocin levels in response to pituitary provocation tests in healthy volunteers

Objective: Oxytocin, secreted into circulation through the posterior pituitary, regulates lactation, weight, and socio-behavioral functioning. Oxytocin deficiency has been suggested in patients with hypopituitarism, however, diagnostic testing for oxytocin deficiency has not been developed. The aim of this study was to investigate known pituitary provocation tests to stimulate plasma oxytocin. Design: 65 healthy volunteers underwent either the hypertonic saline or arginine infusion test, known to stimulate copeptin, or the oral macimorelin test, known to stimulate growth hormone. Plasma oxytocin was measured before and once plasma sodium ≥150mmol/l for the hypertonic saline, after 60 minutes for the arginine infusion and after 45 minutes for the oral macimorelin test (expected peak of copeptin and growth hormone levels, respectively). Primary outcome was change from basal to stimulated oxytocin levels using paired t-tests. Results: As expected, copeptin increased in response to hypertonic saline and arginine infusion (p<0.001), and growth hormone increased to oral macimorelin (p<0.001). Oxytocin increased in response to hypertonic saline infusion from 0.4pg/mL (0.2) to 0.6pg/mL (0.3) (p=0.003) but with a high variance. There was no change to arginine infusion (p=0.4), and a trend to lower stimulated levels to oral macimorelin (p=0.05). Conclusion: Neither the arginine infusion nor the oral macimorelin test stimulate plasma oxytocin levels, whereas there was an increase with high variance upon hypertonic saline infusion. As a predictable rise in most participants is required for a reliable pituitary provocation test, none of the investigated pituitary provocation tests can be recommended diagnostically to identify patients with an oxytocin deficiency.

Oxytocin Levels in Response to Pituitary Provocation Tests in Healthy Volunteers

Background: Oxytocin, secreted into the circulation through the posterior pituitary, regulates lactation, weight, and socio-behavioral functioning. Oxytocin deficiency has been suggested in patients with hypopituitarism, however, diagnostic testing for oxytocin deficiency has not been developed. Known stimuli used in the diagnosis of pituitary deficiencies - the hypertonic saline and arginine infusion tests stimulating copeptin levels, and the oral macimorelin test stimulating growth hormone levels - have also been shown to stimulate oxytocin secretion in animal models. We hypothesized that these provocation tests would stimulate plasma oxytocin levels in humans. Methods: Basal plasma oxytocin levels were measured for all three tests. Stimulated plasma oxytocin was measured once plasma sodium &gt;150 mmol/l for the hypertonic saline and after 45 minutes for the arginine infusion and the oral macimorelin test, expected peak of copeptin and growth hormone levels, respectively. Primary outcome was change between basal and stimulated oxytocin levels using a paired t-test. Results: Median (IQR) age of all participants was 24 years (22, 28), 51% were female. As expected, copeptin increased in response to hypertonic saline from 4.0 pmol/L [3.3, 6.7] to 34.2 pmol/L [23.2, 45.4] (p-value &lt;0.001) and in response to arginine infusion from 4.6 pmol/L [3.2, 6.2] to 8.3 pmol/L [6.4, 10.8] (p-value &lt;0.001). Growth hormone increased in response to oral macimorelin from 1.6 ng/mL [0.3, 17.2] to 106.0 ng/mL [73.3, 127.2] (p-value &lt;0.001). Oxytocin levels increased in response to hypertonic saline infusion from 0.3 pg/mL [0.3, 0.5] to 0.6 pg/mL [0.4, 0.7] (p-value 0.007), while there was no change in response to arginine infusion (basal 0.4 pg/mL [0.4, 0.6], stimulated 0.4 pg/mL [0.3, 0.6], p-value 0.6), nor to oral macimorelin (basal 38.7 pg/mL [31.1, 66.9], stimulated 34.2 pg/mL [31.2, 48.2], p-value 0.3). Conclusion: We found that hypertonic saline infusion results in doubling of oxytocin levels. Further research will be important to determine whether this test could be used diagnostically to identify patients with oxytocin deficiency. In contrast to animal data, arginine and macimorelin did not stimulate oxytocin.

Effect of Arginine on the Hypothalamic–Pituitary–Adrenal Axis in Individuals With and Without Vasopressin Deficiency

Context Arginine stimulates pituitary hormones, like growth hormone and vasopressin, but its effect on the hypothalamic–pituitary–adrenal (HPA) axis is unknown. Arginine may also stimulate the HPA axis, possibly through a mechanism involving vasopressin. Objective To investigate the effect of arginine on adrenocorticotropic hormone (ACTH) and cortisol in subjects with and without vasopressin deficiency. Design Prospective study, University Hospital Basel. Participants 38 patients with central diabetes insipidus, 58 patients with primary polydipsia, and 50 healthy controls. Intervention Arginine infusion with measurement of ACTH, cortisol and copeptin at baseline and 30, 45, 60, 90, and 120 minutes. Results We found different response patterns to arginine: in patients with diabetes insipidus (and low stimulated copeptin levels) median (interquartile range [IQR]) ACTH and cortisol increased from 22.9 (16.8, 38.7) to 36.6 (26.2, 52.1) ng/L and from 385 (266, 463) to 467 (349, 533) nmol/L, respectively. In contrast, median (IQR) ACTH and cortisol levels decreased in patients with primary polydipsia (despite high stimulated copeptin levels): ACTH from 17.3 (12.3, 23) to 14.8 (10.9, 19.8) ng/L and cortisol from 343 (262, 429) to 272 (220.8, 360.3) nmol/L; likewise, in healthy controls: ACTH from 26.5 (17.6, 35.7) to 14.8 (12.1, 22.7) ng/L and cortisol from 471 (393.3, 581.8) to 301.5 (206.5, 377.8) nmol/L. Conclusion Diabetes insipidus is associated with increased responsiveness of ACTH/cortisol to arginine. In contrast, arginine does not stimulate the HPA axis in healthy controls or in primary polydipsia.

Absent increase in vertebral artery blood flow during l-arginine infusion in hypertensive men

Endothelial dysfunction is observed in the peripheral vasculature of hypertensive patients, but it is unclear how the cerebral circulation is affected. More specifically, little is known about the impact of human hypertension on vertebral artery (VA) endothelial function. This study evaluated whether the endothelial function of the VA is impaired in hypertensive men. For 13 male hypertensive subjects (46 ± 3 yr) and eight age-matched male controls (46 ± 4 yr), blood pressure (BP; photoplethysmography), VA, and common carotid (CC) blood flow (duplex ultrasound) were determined at rest and during 30 min of intravenous l-arginine (30 g; a precursor of nitric oxide) or isotonic saline infusion. Controls and hypertensive subjects demonstrated a similar resting CC (601 ± 30 vs. controls 570 ± 43 ml/min; P = 0.529) and VA blood flow (119 ± 11 vs. controls 112 ± 9 ml/min; P = 0.878). During administration of l-arginine, CC blood flow increased similarly between groups (hypertensive 12 ± 3%, controls 13 ± 2%; P = 0.920). In contrast, the increase in VA blood flow was nonexistent in the hypertensive subjects (0.8 ± 3% vs. controls: 16 ± 4%; P = 0.015) with no significant change in BP. Both CC and VA flow returned to near-resting values within 30 min after the infusion, and for four hypertensive subjects and three controls, time-control experiments using 0.9% saline did not affect VA or CC blood flow significantly. The results demonstrate endothelial dysfunction in the posterior cerebral circulation of middle-aged hypertensive men.