d-limonene prevents ultraviolet irradiation: Induced cyclobutane pyrimidine dimers in Skh1 mouse skin

Table 1 Quantitative analysis of the effect of d-limonene on cyclobutane pyrimidine dimer, N-myc downstream regulating gene 1 and proliferating cell nuclear antigen induction

Groups	CPD-positive cells (%)	NDRG1-positive cells (%)	PCNA-positive cells (%)
Control	0.0	6.0 ± 1.4	7.1 ± 1.7
UVR only	94.7 ± 11.1	70.0 ± 10.4	52.4 ± 9.9
UVR + 1.0% d-limonene	45.7 ± 8.3	64.6 ± 9.2	42.9 ± 8.1
UVR + 10% d-limonene	26.6 ± 5.8	16.2 ± 3.4	36.2 ± 6.7
UVR + 100% d-limonene	13.9 ± 4.5	6.3 ± 1.7	13.8 ± 3.4
100% d-limonene alone	0.0	28.1 ± 5.2	74.6 ± 11.1

d-Limonene was administered orally daily for 4 consecutive days prior to 1.5 kJ/m² of UVB radiation. CPD samples were obtained on the 5^th day 5 min after each UVR exposure. Skin samples for NDRG1 and PCNA were obtained 6 d after the UVR exposures. An approximate number of CPD, NDRG1 and PCNA positive cells as well as unstained cells were counted in 3 different areas of equal length for each sample and percentage of positive cells was calculated. UVR: Ultraviolet irradiation; PCNA: Proliferating cell nuclear antigen; NDRG1: N-myc downstream regulating gene 1; CPD: Cyclobutane pyrimidine dimer.