Galactosyl Derivatives of l-Arginine and d-Arginine: Synthesis, Stability, Cell Permeation, and Nitric Oxide Production in Pituitary GH3 Cells

L-Ornithine L-Aspartate Restores Mitochondrial Function and Modulates Intracellular Calcium Homeostasis in Parkinson's Disease Models

The altered crosstalk between mitochondrial dysfunction, intracellular Ca²⁺ homeostasis, and oxidative stress has a central role in the dopaminergic neurodegeneration. In the present study, we investigated the hypothesis that pharmacological strategies able to improve mitochondrial functions might prevent neuronal dysfunction in in vitro models of Parkinson’s disease. To this aim, the attention was focused on the amino acid ornithine due to its ability to cross the blood–brain barrier, to selectively reach and penetrate the mitochondria through the ornithine transporter 1, and to control mitochondrial function. To pursue this issue, experiments were performed in human neuroblastoma cells SH-SY5Y treated with rotenone and 6-hydroxydopamine to investigate the pharmacological profile of the compound L-Ornithine-L-Aspartate (LOLA) as a new potential therapeutic strategy to prevent dopaminergic neurons’ death. In these models, confocal microscopy experiments with fluorescent dyes measuring mitochondrial calcium content, mitochondrial membrane potential, and mitochondrial ROS production, demonstrated that LOLA improved mitochondrial functions. Moreover, by increasing NCXs expression and activity, LOLA also reduced cytosolic [Ca²⁺] thanks to its ability to modulate NO production. Collectively, these results indicate that LOLA, by interfering with those mitochondrial mechanisms related to ROS and RNS production, promotes mitochondrial functional recovery, thus confirming the tight relationship existing between cytosolic ionic homeostasis and cellular metabolism depending on the type of insult applied.

Orally administrated D-arginine exhibits higher enrichment in the brain and milk than L-arginine in ICR mice

D-Amino acids exert various physiological functions and are widely present in animals. However, they are absorbed to a lesser extent than L-amino acids. Little is known about D-arginine (D-Arg); however, its isomer L-Arg serves as a substrate for several metabolites and exhibits various functions including promotion of growth hormone secretion. Milk is the only nutrient source for infants; it plays an important role during their initial growth and brain development. No studies have evaluated the availability of D-Arg in the brain and milk in mammals. Here, we have studied the differential availability of orally administered D- and L-Arg in the brain and milk using ICR mice. Our results revealed that without D-Arg administration, D-Arg was undetectable in both plasma and brain samples. However, the plasma D-Arg was about twice the concentration of L-Arg post administration of the same. In the cerebral cortex and hypothalamus, L-Arg concentration remained almost constant for over period of 90 min after L-Arg treatment. Nevertheless, the L-Arg concentration decreased after D-Arg administration with time compared to the case post L-Arg administration. Contrastingly, D-Arg level sharply increased at both the brain regions with time after D-Arg treatment. Furthermore, L-Arg concentration in the milk hardly increased after L-Arg administration. Interestingly, oral administration of D-Arg showed efficient enrichment of D-Arg in milk, compared with L-Arg. Thus, our results imply that D-Arg may be available for brain development and infant nourishment through milk as an oral drug and/or nutrient supplement.

Galactosylated Pro-Drug of Ursodeoxycholic Acid: Design, Synthesis, Characterization, and Pharmacological Effects in a Rat Model of Estrogen-Induced Cholestasis

Ursodeoxycholic acid (UDCA) is considered the first-choice therapy for cholestatic disorders. To enhance solubility and exploit specific transporters in liver, we synthesized a new galactosyl pro-drug of UDCA (UDCAgal). Ethinylestradiol (EE)-induced cholestasis was used to study and compare the effects of UDCAgal with UDCA on bile flow, hepatic canalicular efflux transporter expression, and inflammation. UDCAgal resulted quite stable both at pH 7.4 and 1.2 and regenerated the parent drug after incubation in human plasma. Its solubility, higher than UDCA, was pH- and temperature-independent. UDCAgal displayed a higher cell permeation compared to UDCA in liver HepG2 cells. Moreover, in cholestatic rats, UDCAgal showed a higher potency compared to UDCA in reducing serum biomarkers (AST, ALT, and ALP) and cytokines (TNF-α and IL-1β). The higher effect of UDCAgal on the increase in bile salt export pump and multidrug resistance-associated protein 2 transcription indicated an improved spillover of bile acids from the liver. UDCAgal showed a reduction in CCL2, as well as TNF-α, IL-1β, and cyclooxygeanse-2 mRNAs, indicating a reduction in hepatic neutrophil accumulation and inflammation. Moreover, UDCAgal, similarly to UDCA, heightens bile flow and modulates biliary acids secretion. These results indicate that UDCAgal has a potential in the treatment of cholestatic disease.

Galactosyl prodrug of palmitoylethanolamide: synthesis, stability, cell permeation and cytoprotective activity

N-Palmitoylethanolamide (PEA) is emerging as a novel therapeutic agent in the treatment of neuropathic pain and neurodegenerative diseases. Unfortunately, PEA poorly reaches the central nervous system (CNS), after peripheral administration, since it is inactivated through intracellular hydrolysis by lipid amidases. Since prodrug approach is one of the most popular methods used to increase cell permeability, the aim of this paper consists in the synthesis of a new galactosyl prodrug of PEA, the palmitoylethanolamide-succinamyl-D-galactos-6'-yl ester (PEAGAL). Biological experiments both in neuroblastoma and in C6 glioma cells, together with quantitative analyses performed through a LC-MS-MS technique, demonstrate the better efficacy of PEAGAL compared to PEA and its higher cell permeation. Our results encourage further experiments in animal models of neuropathic pain and of neurological disorders and/or neurodegenerative diseases, in order to promote a more effective peripherally administrated derivative of PEA.

D-Arginine as a neuroprotective amino acid: promising outcomes for neurological diseases

In humans, as in other mammals, endogenous glucocorticoids (GCs) are essential for adapting to physiological life stress. They are also crucial for the healthy development of the fetus. However, when the physiological concentrations of GCs increase over a long period of time, the central nervous system (CNS) is predisposed to the development of psychiatric disorders and neurological diseases. Here, I discuss the strong influence of GCs on the nitric oxide (NO) pathway and the generation of reactive oxygen species (ROS). I also highlight supporting evidence for the neuroprotective actions of d-arginine (d-Arg) against neurotoxicity induced by high levels of GCs in the CNS. Given that d-Arg does not interfere with the immunosuppressive and anti-inflammatory effects of GCs, this might be a novel way of neutralizing the neurotoxic effects of GCs in the CNS without compromising their positive peripheral actions.

Prodrug design for the potent cardiovascular agent Nω-hydroxy-L-arginine (NOHA): synthetic approaches and physicochemical characterization

N(ω)-Hydroxy-L-arginine (NOHA)--the physiological nitric oxide precursor--is the intermediate of NO synthase (NOS) catalysis. Besides the important fact of releasing NO mainly at the NOS-side of action, NOHA also represents a potent inhibitor of arginases, making it an ideal therapeutic tool to treat cardiovascular diseases that are associated with endothelial dysfunction. Here, we describe an approach to impart NOHA drug-like properties, particularly by wrapping up the chemically and metabolically instable N-hydroxyguanidine moiety with different prodrug groups. We present synthetic routes that deliver several more or less highly substituted NOHA derivatives in excellent yields. Versatile prodrug strategies were realized, including novel concepts of bioactivation. Prodrug candidates were primarily investigated regarding their hydrolytic and oxidative stabilities. Within the scope of this work, we essentially present the first prodrug approaches for an interesting pharmacophoric moiety, i.e., N-hydroxyguanidine.

The galactosylation of N(ω)-nitro-L-arginine enhances its anti-nocifensive or anti-allodynic effects by targeting glia in healthy and neuropathic mice

This study has investigated whether the galactosyl ester prodrug of N(ω)-nitro-L-arginine (NAGAL), shows enhanced analgesic efficacy in healthy mice and in models of visceral and neuropathic pain: the writhing test and the spared nerve injury (SNI), respectively. NAGAL was compared to methyl ester pro-drug of N(ω)-nitro-l-arginine (L-NAME), a widely exploited non-specific nitric oxide synthase (NOS) inhibitor, for analgesic potential. The writhing test revealed that the ED(50) value, along with the 95% confidence limit (CL) was 3.82 (1.77-6.04) mg/kg for NAGAL and, 36.75 (20.07-68.37) mg/kg for L-NAME. Notably, NAGAL elicited a greater anti-allodynic effect than L-NAME did in neuropathic mice. Biomolecular and morphological studies revealed that spared nerve injury increased the expressions of pro-inflammatory enzymes (caspase-1) and two glial cell biomarkers: integrin alpha M (ITGAM) and glial fibrillary acidic protein (GFAP) in the spinal cord. Finally, GLUT-3, an isoform of the hexose transporters capable to bind NAGAL and inducible NOS (iNOS), were found to be over-expressed in the activated astrocytes of the spinal cord of neuropathic mice. NAGAL administration normalized expression levels of these biomarkers. NAGAL showed a greater efficacy in inhibiting visceral pain and allodynia than L-NAME possibly by a greater cell permeation through the hexose transporter which is highly over-expressed by activated glia.