Why caffeine is easily oxidized to uric acid?
I doubt caffeine can be so easily oxidized to uric acid. I'd propose a way by demethylation via cytochrome P450 to the corresponding xanthines and oxidation via xanthine oxidase (but these are enzymatic reactions).

From a synthetic perspective, one will start with guanine (-> guanine deaminase followed by oxidation; or oxidative deamination of Guanine followed by another oxidation)

It's not safe to conclude that caffeine increase uric acid blood level.

Long story short:
Coffee consumption seems to lower uric acid blood levels.
Decaf coffee consumption also seems to lower uric acid blood levels.
Tea consumption seems to have no effect on uric acid blood levels.


  Serum uric acid level tended to decrease with increasing coffee intake
  (Figure 1). After adjusting for age and sex, serum uric acid level in
  individuals with coffee intake 6 cups daily was lower than in those
  with no use by
  0.43 mg/dl (95% CI 0.22, 0.65; P for trend  0.001). After adjusting for other covariates, the differences were attenuated but remained
  significant (P for trend  0.001) (Table 2).


"Coffee, Tea, and Caffeine Consumption and Serum Uric Acid Level: The Third National Health and Nutrition Examination Survey", Choi HK, Curhan G., 2007
DOI 10.1002/art.22762

It has to be noted this was the first study I found on the fly and there may be other results out there