In vitro activation of immune lymph node cell proliferation by photohapten-modified cells in murine contact photosensitivity

Induction of keratinocyte apoptosis by photosensitizing chemicals plus UVA

BACKGROUND

The capacity of photosensitizing chemicals with ultraviolet A light (UVA) to induce apoptosis is one of the methods to assess their phototoxic and potentially photoallergic properties, since apoptotic cells may be easily presented by antigen-presenting cells.

OBJECTIVES

We examined the photoaggravated ability to induce keratinocyte apoptosis of various chemicals that are known as causative agents of photocontact dermatitis and drug photosensitivity involving photoallergic and/or phototoxic mechanisms.

METHODS

HaCaT keratinocytes were incubated with 3,3',4',5-tetrachlorosalicylanilide (TCSA), bithionol, diphenylhydramine, chlorpromazine, 6-methylcoumarin, sparfloxacin, and enoxacin at 10(-7) to 10(-4)M and irradiated with UVA at 4J/cm(2). As positive control, 8-methoxypsoralen (8-MOP) was also tested. Apoptosis and necrosis were evaluated by flow cytometric enumeration of annexin V(+) 7-AAD(-) and annexin V(+) 7-AAD(+) cells, respectively. The expression of apoptosis-related molecules, caspase-3 and poly (ADP-ribose) polymerase (PARP), was tested by flow cytometric and Western blotting analyses.

RESULTS

In a comparison with non-irradiated cells, significant apoptosis was found in TCSA, bithionol, chlorpromazine, sparfloxacin and enoxacin at 10(-4) or 10(-5)M as well as 8-MOP as assessed by both annexin V and active caspase-3 stainings, while necrosis occurred in most of these chemicals at 10(-4)M. Neither apoptosis nor necrosis was seen in diphenylhydramine or 6-methylcoumarin. PARP were activated in HaCaT cells phototreated with TCSA, bithionol and chlorpromazine.

CONCLUSIONS

We suggest that our method is useful for in vitro assessment of phototoxicity and potential photoallergenicity of chemicals.

Photohaptenic properties of fluoroquinolones

Although quinolone antibacterial agents have both phototoxicity and photoallergenicity, the latter's potency has been poorly investigated compared with the former's. Some of the photoallergic chemicals serve as photohaptens, which lead to T-cell-mediated immune reactions after photobinding to protein by UVA radiation. We examined the photohaptenic potential of fluoroquinolones, including lomefloxacin (LFLX), ciplofloxacin, norfloxacin, ofloxacin, levofloxacin, fleroxacin, enoxacin and sparfloxacin (SPFX). The absorption spectra of the quinolones were altered by UVA irradiation, with an exception of SPFX that seems to be photostable toward UVA. Bovine serum albumin and murine epidermal cells were coupled with these fluoroquinolones other than SPFX by exposure to UVA. Subcutaneous inoculation of fluoroquinolone-photomodified epidermal cells induced and elicited a delayed-type hypersensitivity reaction in mice. However, epidermal cells incubated with LFLX without UVA exposure also induced and elicited a significant hypersensitivity reaction to a lesser degree than LFLX-photomodified epidermal cells. Furthermore, there was cross-reactivity between LFLX-photomodified epidermal cells and simply LFLX-incubated cells. This suggests that cells can be weakly modified with LFLX even in the dark and that UVA irradiation promotes this modification. Our study demonstrated that fluoroquinolones have photohaptenic properties to which their photoallergenicity is probably ascribed.

Afloqualone photosensitivity: immunogenicity of afloqualone-photomodified epidermal cells

Afloqualone (AQ) is an oral muscle relaxant and evokes ultraviolet A (UVA)-induced photosensitivity dermatitis as a side effect. Histologic observations of the skin eruption suggest that AQ photosensitivity is mediated not only by phototoxic but also by photoallergic mechanisms. To address the immunological mechanisms of AQ photosensitivity, we examined the immunogenicity of AQ-photomodified epidermal cells in mice. Afloqualone was covalently coupled with bovine serum albumin by irradiation with UVA but not UVB. Because of this ability of AQ to photobind to protein, murine epidermal cells were easily modified with AQ by exposure to UVA. Subcutaneous inoculation of AQ-photomodified epidermal cells successfully induced an antigen-specific delayed-type hypersensitivity in mice. These findings suggest that AQ-photoderivatized epidermal cells are highly immunogenic and that photomodification of epidermal cells with AQ is an initial event to evoke AQ photosensitivity dermatitis.

Evaluation of ultraviolet-A protection by sunscreen agents using a mouse model of contact photoallergy

This study was conducted to investigate in vivo evaluation of protectiveness by sunscreens in the UVA range using a mouse model of contact photoallergy (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA). Mice were sensitized with TCSA painting plus UVA irradiation (TCSA/UVA) on the abdomen and, 5 days later, challenged with TCSA/UVA on the earlobe. Each of four sunscreen agents, benzophenone-3, Parsol 1789, p-aminobenzoic acid, and 2-ethyl-hexyl-p-methoxycinnamate, was applied to the earlobes before irradiation. Their protective efficacy was evaluated in the degree of inhibition of both ear swelling responses and TCSA-epidermal cell photoadduct formation. Two UVA-absorbing sunscreens, benzophenone-3 and Parsol 1789, dramatically inhibited the ear swelling response, while the two UVB-absorbers exhibited a much less suppressive effect. The UVA-absorbing agents functioned via inhibiting the formation of TCSA-epidermal cell photoadducts. This method is thought to be useful for in vivo estimation of UVA protection provided by sunscreens against the exquisite sensitivity involved in photoallergy.

Inhibitory effect of melanin pigment on sensitization and elicitation of murine contact photosensitivity: mechanism of low responsiveness in C57BL/10 background mice

We have shown that murine contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) is genetically controlled mainly by the major histocompatibility complex. The H-2b,d haplotypes are closely associated with high responders, whereas mice with the H-2k are non-responders. Irrespective of their H-2 haplotypes, the C57BL/10 (B10) background strains, including B10, B10.D2, B10.A, and B10.BR, possessing black fur color, were low or nonresponders in CPS to TCSA. In B10 mice, however, high-sensitivity responses were induced when subcutaneous inoculation of epidermal cells (ECs) photomodified in vitro with TCSA was used for both immunization and challenge, suggesting that the epicutaneous route for induction and elicitation is defective in B10 background mice. F1 mice obtained by crossing high-responder BALB/c and low-responder B10 mice, possessing agouti fur color, were non-responders of CPS. The magnitude of CPS in the F2 mice derived from F1 (BALB/c X B10) siblings varied from low to high. When these F2 mice were divided into five groups with regard to fur color, the magnitude of reaction was correlated with the fur color and there was inverse relationship between the magnitude of CPS and the amount of melanin pigment in earlobe ECs. Furthermore, the in vivo formation of TCSA-EC photoadducts was negatively correlated to the melanin amount in earlobes. These observations suggested that the failure in CPS of the B10 background mice stems from inability of in vivo photocoupling of TCSA to ECs, presumably due to absorption of ultraviolet radiation by melanin pigment.

A cross-reaction between piroxicam-photosensitivity and thiosalicylate hypersensitivity in lymphocyte proliferation test

We examined the cross-reaction between photosensitivity to piroxicam (PXM) and contact sensitivity to thiosalicylate (TOS) by a lymphocyte proliferation test (LPT) in guinea pigs. The lymph node cells (LNCs) plus peritoneal exudate cells (PECs) from guinea pigs contact-sensitized with TOS remarkably cross-proliferated to PXM under UVA (4 J/cm2) irradiation. On the other hand, the PXM-photosensitized LNCs+PECs also cross-proliferated to TOS. From these results, the reciprocal cross-reaction between TOS-hypersensitivity and PXM-photosensitivity was reconfirmed by the in vitro LPT, indirectly indicating that the PXM-photosensitivity is a cell (probably T cell)-mediated PXM photoallergy in its nature. The TOS-primed LNCs+PECs did not cross-proliferate to UVA (4 J, 180 J or 500 J/cm2)-pretreated PXM (UVA-PXM) although it is supposed to contain several photoproducts of PXM. Furthermore, the TOS-primed LNCs developed a remarkable proliferative cross-response to the PECs pulsed with PXM under UVA (4 J/cm2) irradiation (photo-PXM-modified PECs), but not to the PECs pulsed with PXM or UVA-PXM. Therefore, it is presumed that the cross-reactive molecule, which is easily formed from PXM under UVA irradiation, is unstable, and that the formation of complete antigen by the generation of this molecule and its photobinding needs the coexistence of PECs, PXM and UVA irradiation at the same time in the culture.