The significance of the arginine and arginase of tears in experimentally-induced herpes simplex corneae

L-lysine: its antagonism with L-arginine in controlling viral infection. Narrative Literature Review

Knowledge about viral characteristics, mechanisms of entry into the host cell and multiplication/dissemination can help in the control and treatment of viral pathologies. Several nutritional factors linked to the host may favor viral multiplication and their control, may lead to new prophylactic alternatives and/or antiviral therapies. The objective of this review is to discuss the relationship between the amino acid L-lysine and the control of viral infections, aiming at a possible therapeutic property. This research used databases such as PubMed, Web of Science, Scielo, Medline and Google Scholar, as well as searching for references cited by journals. The time frame covered the period between 1964 and January 2022. The observed studies have shown that the usual antiviral therapies are not able to interfere with the viruses in their latent state, however, they can interfere with the adhesion and fusion of viral particles or the production of proteins, which play an important role in viral epidemiology and control, particularly in the initial moment and in the reactivation. Lysine is an amino acid that can interfere mainly in the formation of capsid proteins and DNA by a competitive antagonism with amino acid arginine, which is an essential amino acid for some viruses and also by promoting the increase of arginase, increasing the catabolism of arginine. Although there is evidence of the importance of L-lysine in viral control, more studies are needed, with a view to new antiviral therapies.

Recurrent Herpes Zoster Ophthalmicus Preceded by Anabolic Steroids and High-Dose L-Arginine

PURPOSE

To report a case of a 34-year-old male with recurrent herpes zoster ophthalmicus (HZO) preceded by a 6-week cycle of anabolic steroids and high-dose amino acid supplementation. Case Presentation. A 34-year-old man presented to our institution for left eye pain for one week associated with a vesicular rash in the V1 dermatome, respecting the midline. The patient had no significant past medical or past ocular history, including systemic immunosuppressive agents or HIV. However, prior to the onset of his symptoms the patient had completed a 6-week course of anabolic steroids including trenbolone, deca-durabolin, and testosterone as well as high-dose arginine supplementation averaging more than 40 grams a day. The best-corrected vision was 20/25 OS with slit-lamp examination remarkable for punctate staining and pseudodendrites at 6 o'clock, outside the visual axis. The patient was treated with oral acyclovir 800 mg five times a day for seven days along with prednisolone QID and moxifloxacin QID which was tapered over a month. Four months after resolution, the patient developed a recurrent HZO keratitis preceded by another cycle of anabolic steroids and amino acid supplementation.

CONCLUSION

In vitro L-arginine supplementation has been associated with the proliferation and virulence of a variety of herpes viruses. Anabolic steroids have also been demonstrated by various studies to negatively affect cell-mediated immunity necessary to prevent viral infection. Thus, it is possible that anabolic steroids in conjunction with increased L-arginine intake may have precipitated a recurrent HZO in a previously healthy, immunocompetent individual.

Recurrent herpes zoster ophthalmicus in a young, healthy individual taking high doses of l-Arginine

Purpose

To report a case of a healthy, young male with recurrent herpes zoster ophthalmicus (HZO) and high-dose l-arginine supplementation.

Observations

A 39-year-old man presented to another institution with a HZO involving the right eye. He was treated with oral acyclovir with complete resolution. Four months later the patient had a recurrent HZO episode and was started again on oral acyclovir. After resolution of the episode, the patient was continued on 1 g of oral acyclovir daily as a prophylactic measure. He then presented to our institution for a second opinion. The patient was otherwise healthy, with no past medical history involving systemic immunosuppressant agents or HIV. However, the patient was an active weight lifter taking high doses of amino acids. A diet recall was performed prior to both HZO episodes, which calculated an average intake of 46.5 g of l-arginine a day. Examination revealed 20/40 best-corrected acuity, anterior stromal haze in the visual axis, and inferior superficial punctate keratitis in the right eye. The patient was treated for dry eye disease with punctual plugs and artificial tears. The patient was instructed to decrease all supplemental arginine consumption while continuing with oral acyclovir prophylaxis for one year.

Conclusions and importance

l-arginine is associated with the replication and virulence of a variety of viruses in vitro, including herpes simplex and varicella zoster. Although arginine consumption increased prior to the initial and recurrent HZO infection, further investigation needs to be performed to deem if a true association exists.

Development and evaluation of a host-targeted antiviral that abrogates herpes simplex virus replication through modulation of arginine-associated metabolic pathways

Since their inception five decades ago, most antivirals have been engineered to disrupt a single viral protein or process that is essential for viral replication. This approach has limited the overall therapeutic effectiveness and applicability of current antivirals due to restricted viral specificity, a propensity for development of drug resistance, and an inability to control deleterious host-mediated inflammation. As obligate intracellular parasites, viruses are reliant on host metabolism and macromolecular synthesis pathways. Of these biosynthetic processes, many viruses, including Herpes simplex viruses (HSV), are absolutely dependent on the bioavailability of arginine, a non-essential amino acid that is critical for many physiological and pathophysiological processes associated with either facilitating viral replication or progression of disease. To assess if targeting host arginine-associated metabolic pathways would inhibit HSV replication, a pegylated recombinant human Arginase I (peg-ArgI) was generated and its in vitro anti-herpetic activity was evaluated. Cells continuously treated with peg-ArgI for over 48 h exhibited no signs of cytotoxicity or loss of cell viability. The antiviral activity of peg-ArgI displayed a classical dose-response curve with IC50's in the sub-nanomolar range. peg-ArgI potently inhibited HSV-1 and HSV-2 viral replication, infectious virus production, cell-to-cell spread/transmission and virus-mediated cytopathic effects. Not unexpectedly given its host-targeted mechanism of action, peg-ArgI showed similar effectiveness at controlling replication of single and multidrug resistant HSV-1 mutants. These findings illustrate that targeting host arginine-associated metabolic pathways is an effective means of controlling viral replicative processes. Further exploration into the breadth of viruses inhibited by peg-ArgI, as well as the ability of peg-ArgI to suppress arginine-associated virus-mediated pathophysiological disease processes is warranted.

Enzymes of urea synthesis are expressed at the ocular surface, and decreased urea in the tear fluid is associated with dry-eye syndrome

PURPOSE

The present study aims at determining whether enzymes of urea synthesis are expressed in the human lacrimal gland and in tissues of ocular surface (conjunctiva, cornea), to give evidence for the hypothesis that urea can be locally formed from ocular tissues and is important for the composition of the tear fluid.

METHODS

The presences of enzymes (arginase 1, 2 and agmatinase) that directly contribute to the formation of urea were investigated in the lacrimal gland and tissues of ocular surface by RT-PCR and immunohistochemistry. We collected tear fluid, aqueous humour, and blood samples from a total of 38 subjects, and tear fluid samples from a total of 78 subjects, with and without dry-eye syndrome (DES, keratoconjunctivitis sicca), and determined the urea concentration.

RESULTS

The enzymes arginase 1, 2 and agmatinase were expressed in all tissues examined except for arginase 1, which was not expressed in the cornea. There was no correlation of urea concentration in tear fluid with aqueous humour and blood plasma (r = 0.13, p = 0.58 and r = 0.45, p = 0.05 respectively). However, correlation of urea concentration between aqueous humour and blood plasma was highly significant (r = 0.7, p = 0.0001). The concentration of urea in the tear fluid of patients with DES compared to healthy control group was significantly reduced (p < 0.0001).

CONCLUSION

Enzymes that are directly involved in the formation of urea are expressed in ocular tissues. This may imply that in the ocular surface is a well-coordinated system of enzymes that can produce urea which might be independent of external urea supply.

Land use, macroalgae, and a tumor-forming disease in marine turtles

Wildlife diseases are an increasing concern for endangered species conservation, but their occurrence, causes, and human influences are often unknown. We analyzed 3,939 records of stranded Hawaiian green sea turtles (Chelonia mydas) over 28 years to understand fibropapillomatosis, a tumor-forming disease linked to a herpesvirus. Turtle size is a consistent risk factor and size-standardized models revealed considerable spatial and temporal variability. The disease peaked in some areas in the 1990s, in some regions rates remained constant, and elsewhere rates increased. Land use, onshore of where the turtles feed, may play a role. Elevated disease rates were clustered in watersheds with high nitrogen-footprints; an index of natural and anthropogenic factors that affect coastal eutrophication. Further analysis shows strong epidemiological links between disease rates, nitrogen-footprints, and invasive macroalgae and points to foraging ecology. These turtles now forage on invasive macroalgae, which can dominate nutrient rich waters and sequester environmental N in the amino acid arginine. Arginine is known to regulate immune activity, promote herpesviruses, and contribute to tumor formation. Our results have implications for understanding diseases in aquatic organisms, eutrophication, herpesviruses, and tumor formation.

Utilization of lacrimal urea assay in the monitoring of hemodialysis: conditions, limitations and lacrimal arginase characterization

The lacrimal urea content was found to be proportional to that of blood, which suggested its possible utilization in the monitoring of hemodialysis as a less invasive method. On the other hand, however, arginase activity was detected in tears, which may influence the urea content independently of blood urea concentration. The feasibility of using lacrimal urea measurement to replace blood urea measurement in the monitoring hemodialysis was also investigated. Blood and tear samples of 35 healthy persons and 43 renal patients undergoing hemodialysis were tested. Tear samples were collected on Schirmer paper strips. After elution the lacrimal urea content was measured by a colorimetric method. The determination of arginase activity was based on the release of urea and ornithine. The correlation between blood and lacrimal urea and arginase was studied by multivariate regression analysis. The lacrimal arginase isoenzyme pattern was investigated by native polyacrylamide gel electrophoresis and Western blotting. The effect of partially isoform-specific inhibitors was also studied. Blood urea levels in blood were significantly higher in the renal patients before dialysis than in the control patients (12.86 +/- 0.59 vs. 6.45 +/- 0.41 mM, p < 0.0001). Blood sera arginase activity was very low. Lacrimal arginase activity was significantly higher in tears than in sera (p < 0.0001 for each group). The tear/serum ratio of urea content was significantly different between controls and renal patients, particularly in postdialytic samples (1.89 +/- 0.07 vs. 3.49 +/- 0.31, p < 0.0001). The correlation between lacrimal and blood sera urea was best in controls (r = 0.89) and was better in predialytic (r = 0.75) than in postdialytic (r = 0.52) samples, depending on the level of arginase activity. In postdialytic samples a stronger correlation (r = 0.77) between tear urea and arginase was observed. Both arginase isoforms were detected in tears, but the extrahepatic (arginase II) isoenzyme was present in higher concentration. In conclusion, the determination of lacrimal urea level as a possible less invasive replacement for blood urea determination could only be utilized in the monitoring of hemodialysis if lacrimal arginase is also measured. Blood urea levels can be correctly determined by using equations, which take into account arginase activity. The accuracy of these equations was checked on a new patient population. Both arginase isoenzymes were observed in lacrimal samples.

Biochemical analysis of arginase and ornithine carbamoyltransferase in human vitreous humor

BACKGROUND

The presence of arginase and ornithine carbamoyltransferase (OTC'ase) enzymes in human vitreous humor after death was investigated in this study. To the best of our knowledge, there is no prior report on the activity of arginase or ornithine carbamoyltransferase in human vitreous humor.

METHODS

The presence of arginase and OTC'ase activities were examined in the human vitreous humor of 19 samples. Spectrophotometric methods were used to determine activities of arginase and OTC'ase.

RESULTS

Arginase activity was detected in human vitreous humor, whereas OTC'ase activity was below the detection limit. Therefore, we focused on biochemical analysis of arginase in human vitreous humor. Kinetic properties of arginase activity in vitreous humor were optimized. In contrast to other arginases, optimal preincubation temperature and pH were 40 degrees C and 8.8, respectively. Km of vitreous arginase for L-arginine was 6 mM. Preincubation of the enzyme with Mn(2)+ ions caused a significant increase (33%) in arginase activity.

CONCLUSIONS

The activity and presence of arginase as well as its kinetics in human vitreous are documented in this study. Biochemical functions and the importance of arginase in vitreous humor are not well understood. However, its presence may be explained by means of its involvement in polyamine biosynthesis as observed in the other extrahepatic tissues.

Induction of arginases I and II in cornea during herpes simplex virus infection

Induction of inducible nitric oxide synthase (iNOS) following corneal infection with herpes simplex virus type-1 (HSV-1) generates nitric oxide (NO), an important player in the defense against viral infection. Changes in arginine metabolism during infection are not limited to effects of iNOS but can also involve arginases, which can modulate NO synthesis and produce ornithine for the generation of polyamines and proline. The latter are important molecules involved in tissue damage and repair during inflammation. In this study we determined the responses of arginase I and II in a murine model of HSV-1-induced stromal keratitis (HSK). In the cornea iNOS and arginase II mRNA were co-induced as the initial inflammation developed at 2 days postinfection (p.i.). As stromal keratitis progressed (days 8-15 p.i.) arginase I mRNA was induced tenfold, in contrast to a moderate decrease in arginase II and a loss of iNOS expression. These results suggest that elevated expression of arginase I and II in the cornea at late stages of ocular HSV-1 infection may play a role in lesion expression in HSK.