Uric acid, an important antioxidant contributing to survival in termites

Abstract

Reactive oxygen species (ROS) are generated spontaneously in all organisms and cause oxidative damage to biomolecules when present in excess. Accumulated oxidative damage accelerates aging; enhanced antioxidant capacity may be a positive factor for longevity. Recently, numerous studies of aging and longevity have been performed using short-lived animals, however, longevity mechanisms remain unknown. Here we show that a termite Reticulitermes speratus that is thought to be long-lived eusocial insect than other solitary insects uses large quantities of uric acid as an antioxidant against ROS. We demonstrated that the accumulation of uric acid considerably increases the free radical-scavenging activity and resistance against ultraviolet-induced oxidative stress in laboratory-maintained termites. In addition, we found that externally administered uric acid aided termite survival under highly oxidative conditions. The present data demonstrates that in addition to nutritional and metabolic roles, uric acid is an essential antioxidant for survival and contributes significantly to longevity. Uric acid also plays important roles in primates but causes gout when present in excess in humans. Further longevity studies of long-lived organisms may provide important breakthroughs with human health applications.

Fig 1. Strong antioxidants in termites Reticulitermes speratus.

(A) Free radical scavenging activities in various species of insects; soluble extracts from R. speratus, mantis (Tenodera aridifolia), fruit fly (Drosophila melanogaster), silkworm (Bombyx mori), hornet (Vespa simillima) and ant (Pristomyrmex punctatus) were used for DPPH radical scavenging assays. Male–female, male–female paired young primary reproductives; Female–female, female–female paired young primary reproductives. Black boxes indicate male and grey boxes indicate female (n = 3–6). (B) The antioxidant activity of termite soldiers after the control, heat (boiled), and proteinase (Pro K) treatments (n = 3–6). (C) The ascorbic acid contents of termite workers and soldiers (n = 3). (D) Data are presented as means ± s.e.m. Statistical significance was assayed using the unpaired t-test followed by Holm’s adjustment [no significance (ns)].

Fig 2. Function of termite antioxidant in the body.

(A) Resistance properties of termites against ultraviolet (UV) irradiation; Fluorescence intensities were increased following UV irradiation of termite workers which had lower antioxidant content than termite soldiers; White scales indicate 1 mm. (B) The panel shows fluorescence quantification (n = 6–9). (C) Termite antioxidant activities during captivity in the laboratory; termite workers were maintained in the open (loosely fitted; white) or closed (sealed with tape; black) dish (n = 3). (D) Protective effects of termite antioxidants against lipid peroxidation; lipid peroxidation products were lower in termite workers that had been maintained for 5 weeks than in those that were collected immediately after UV irradiation (n = 3). Data are presented as means ± s.e.m. Statistical significance was assayed using the unpaired t-test followed by Holm’s adjustment: *P < 0.05; **P < 0.01.

Fig 3. Detection and characterisation of the termite antioxidant.

(A) Chromatogram from HPLC analyses and (B) free radical scavenging activities of collected samples fractionated by HPLC; the evident peak of activity was meshed with the highest peak of the HPLC chromatogram. (C) MS-spectra from LC-MS/MS analyses; fragment ion peaks of standard uric acid (upper panel) were completely matched with those of samples from termite soldiers (lower panel).

Fig 4. Uric acid contributes to the survival of termite worker under laboratory conditions.

(A) Survival rates of termite workers following allopurinol administration for 10 days. (B) Effects of allopurinol and/or uric acid administration on termite survival rates; Feeding of termite workers with the uric acid synthesis inhibitor allopurinol resulted in decreased survival rates (red line). Treatment with allopurinol and uric acid dramatically arrested allopurinol-mediated decreases in survival rates (blue line; n = 270). All treatment groups differed significantly P < 0.001, except that no differences were identified between control (black line) and allopurinol + uric acid groups. (C) Uric acid contents (upper panel) and antioxidant activities (lower panel) of treatment groups at 8 days (n = 3). All error bars represent means ± SEM. Statistical significance was assayed using the unpaired t-test followed by Holm's adjustment: *P < 0.05, **P < 0.01. (D) Feeding of termite workers with paraquat resulted in decreased survival rates (red line); however, co-treatment with uric acid dramatically rescued paraquat-induced reductions in survival rates (blue line; n = 90). All comparisons revealed significant differences (P < 0.001), except for that between the control group and the uric acid group. P values were obtained using log-rank tests (Peto–Peto test and Cochran–Mantel–Haenszel test) and Peto–Prentice–Wilcoxon tests.