Immediate Inflammatory Responses to Adenovirus-Mediated Gene Transfer in Rat Salivary Glands

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Abstract
Although replication-deficient adenoviruses can efficiently transfer genes to the salivary glands, the current vectors precipitate an immediate, transient decrease in salivary function. To study the cause of this salivary hypofunction, 106–1010 plaque-forming units (pfu) of the vector AdCMVβgal were delivered by retrograde ductal infusion to the submandibular glands (SMGs) of rats. Microscopic analysis of infected glands showed a dose-related, rapidly developing inflammatory response, which at the highest amount of virus was characterized by a predominantly neutrophil-containing infiltrate, focal necrosis, and edema. Moreover, the glands of nude rats developed similar morphologic changes to those of immunocompetent rats. After 3 days, the volume of stimulated saliva secreted from SMGs receiving AdCMVβgal (6.75 × 109 pfu) was ~ 20% that of controls. UV-inactivated virus caused a similar decrease in saliva output. We evaluated to what extent the anti-inflammatory glucocorticoid, dexamethasone, could suppress inflammation and preserve salivary function. Three days after infusion with a high dose of AdCMVβgal (6.75 × 109 pfu), the glands from dexamethasone-treated animals showed markedly less inflammation and no necrosis. Furthermore, there was no significant difference in the average amount of saliva secreted from the infected glands (105 ± 17 μl) compared to the control glands (123 ± 18 μl). In addition, dexamethasone extended the expression of β-galactosidase in the SMGs. These results suggest that the adenovirus-mediated acute inflammation in rat SMG is responsible for diminished gland function and transgene expression. Furthermore, we demonstrate a useful role for glucocorticoids in controlling acute inflammation during experimental gene transfer with current adenovirus vectors. Although replication-deficient adenoviruses can efficiently transfer exogenous DNA directly to the salivary glands, the current adenovirus vectors cause an immediate transient decrease in salivary function. Morphological appearance and salivary function were evaluated in rat submandibular glands given increasing doses of AdCMVβgal. Microscopic analysis of infected glands showed a dose-dependent acute inflammation leading to marked destruction of salivary gland tissues. On average, glands infected with high doses of the vector secreted 20% the volume of saliva of the noninfected glands. Daily administration of the glucocorticoid, dexamethasone, was able to limit the inflammation and prevent the dose-related tissue destruction. Moreover, dexamethasone treatment permitted normal salivary flow while increasing the length of transgene expression.