**2. Oxalate formation from ascorbic acid**

Ascorbic acid metabolism is closely linked to its antioxidant function. Circulating ascorbic acid loses two electrons respectively. The intermediate compound formed by the loss of the first electron is an ascorbate radical, which is a type of free radical. The ascorbate radical is stable and non-reactive compared to other radicals. The loss of the second electron results in the oxidized product dehydroxy ascorbic acid. Dehydroxy ascorbic acid can be non-enzymatically converted to unstable and open-chain diketogluconic acid. The breakdown of diketogluconic acid results in the formation of oxalate [13, 14] (**Figure 1**).
