Sexual Dimorphism in Alternative Metabolic Pathways of L-Arginine in Circulating Leukocytes in Young People with Type 1 Diabetes Mellitus

ABSTRACT

Background: Sexual dimorphism in specific biochemical pathways and immune response, underlies the heterogeneity of type 1 diabetes mellitus (T1DM) and affects the outcome of immunotherapy. Arginase and nitric oxide (NO) synthase (NOS) metabolize L-arginine and play opposite roles in the immune response and autoimmune processes.

Objective: We hypothesized that the above mentioned enzymes can be involved in sex and age differences in T1DM and its treatment. Based on this, the enzymes have been studied in peripheral blood leukocytes (PBL) and plasma of young people with T1DM.

Methods: Patients were recruited from Muratsan University Hospital (Yerevan, Armenia) and were divided into groups: girls and boys by age, from children to adolescents and adolescents/young adults with recent-onset T1DM (RO-T1DM) (0.1–1 years) and long-term T1DM (LT-T1DM) (1.6–9.9 years). Arginase activity was assessed by L-arginine-dependent production of L-ornithine, and the NOS activity was assessed by NO/nitrite production. Glycemic control was assessed using hemoglobin A1c test. Plasma HbA1c concentration below 7.5% (median (range) 6.7 [6.2–7.5]) was taken as good glycemic control (+) and above 7.5% (median (range) 10.5 [7.6–13]) as poor glycemic control (-). Healthy volunteers with corresponding sex and age were used as the control group.

Results: All the patients with RO-T1DM, with poor glycemic control, had increased arginase activity in the cytoplasm (cARG) and mitochondria (mARG) in PBL. In girls with RO-T1DM, with good glycemic control, the subcellular arginase activity decreased, and normalized in LT-T1DM, regardless of age. In contrast, boys from both age groups showed high arginase activity, regardless of glycemic control and duration of T1DM along with insulin therapy. At the same time, a significant decrease in the subcellular production of bioavailable NO was observed in children/preadolescents, regardless of glycemic control and duration of diabetes. In adolescents/young adult boys with RO-T1DM, with (-), the subcellular production of NO decreased significantly, and with LT-T1DM, the decrease was attenuated, but even with (+) remained lower than in healthy people. In contrast, in the group of same age girls with RO-T1DM, NO production increased above normal in both cellular compartments, while with LT-T1DM it normalized in the cytoplasm. In adolescents/young adults with LT-T1DM, NO production in PBL mitochondria decreased by almost a half, regardless of glycemic control and gender. Changes in the metabolic pathways of L-arginine in plasma differed and were less substantial than in the PBL cellular compartments in T1DM.

Conclusions: Glycemic status and duration of T1DM along with insulin therapy affect the activity of arginase and NOS-dependent production of bioavailable NO in the cytoplasm and mitochondria in PBL of young patients with T1DM, depending on sex and age. Arginase and NOS can directly affect the processes occurring in the pancreas and the outcome of therapy through infiltrated leukocytes. Obtained data can be useful for understanding the heterogeneity of T1DM and using it to develop available criteria for assessing the severity and treatment of autoimmune diabetes.

KEYWORDS:

• Arginase
• glycemic status
• nitric oxide synthase
• sexual dimorphism
• type 1 diabetes mellitus

Abbreviations

ADA: American Diabetes Association; cARG: Cytoplasmic arginase; mARG: Mitochondrial arginase; HbA1c: Glycated hemoglobin; NO: Nitric oxide; NOS: Nitric oxide synthase; PBL: Peripheral blood leukocyte; LT-T1DM: Long-term type 1 diabetes mellitus; ROS: Reactive oxygen species; RO-T1DM: Recent-onset type 1 diabetes mellitus; T1DM: Type 1 diabetes mellitus

Acknowledgments

The authors greatly thank Ms. Ani Hakobyan (Master of English language and literature) for editing the manuscript.

Author contributions

NA, EA and GK initiated the study, supervised the project, and assisted in interpretation and in writing the manuscript. Experimental analysis was performed by NM, AM, MH and GM. NA and EA carried out interpretation and wrote the manuscript. GM carried out statistical analysis. GK supervised the study and assisted in writing the manuscript. VSh assisted in laboratory measurements. All authors had full access to all the data and participate in their analysis and interpretation. All authors have approved the final version of manuscript.

Disclosure Statement

The authors report no conflicts of interest.