Human Parathyroid Hormone Is Secreted Primarily into the Bloodstream After Rat Parotid Gland Gene Transfer

Abstract

Hypoparathyroidism is a hormone deficiency syndrome that leads to low blood calcium levels and for which current replacement therapy is inadequate. Gene transfer to salivary glands leads to safe and abundant secretion of therapeutic protein into either saliva or the bloodstream. We previously reported the successful transduction of rat submandibular glands with an adenoviral vector encoding human parathyroid hormone (Ad.hPTH), but unfortunately most of the hPTH was secreted into saliva. Because submandibular and parotid glands are morphologically and functionally different, we hypothesized that hPTH sorting might be different in parotid glands. After 2 days, the pattern of hPTH secretion from transduced parotid glands of intact rats was reversed from that of transduced submandibular glands, that is, most transgenic hPTH was detected in serum (5Â10 10 viral particles per gland; the saliva-to-serum ratio of total hPTH secreted was 0.04). Vector copies were localized to the targeted parotid glands, with none detected in liver or spleen. Ad.hPTH next was administered to parotid glands of parathyroidectomized rats. Two days after delivery no hPTH was detectable in saliva, but high levels were found in serum, leading to normalization of serum calcium and a significant increase in the urinary phosphorus-to-creatinine ratio. This study demonstrates for the first time differential sorting of transgenic hPTH between submandibular and parotid glands, suggesting that hPTH may be a valuable model protein for understanding the molecular basis of transgenic secretory protein sorting in these exocrine glands. We also show the clinical potential of salivary gland hPTH gene therapy for patients with hypoparathyroidism.

Gene delivery in salivary glands: From the bench to the clinic

“…Over the last ~15 years we have studied the concept of employing salivary glands as a surrogate endocrine organ using several model human proteins, including α-1-antitrypsin (α1AT), erythropoietin (Epo), growth hormone (GH) and parathyroid hormone (PTH) [4,7,12, 23,24]. While results with α1AT and GH have been relatively straightforward, studies with Epo and PTH were not predictable, with differences in their secretory behavior occurring between certain species and gland types [e.g., 12,23–27].…”

“…While results with α1AT and GH have been relatively straightforward, studies with Epo and PTH were not predictable, with differences in their secretory behavior occurring between certain species and gland types [e.g., 12,23–27]. Unfortunately, little is known about the mechanisms responsible for the sorting of secretory proteins in polarized epithelial cells.…”

“…Salivary gene delivery has been shown to be useful or potentially useful for the repair [28,29] and prevention [30–32] of radiation damage, the treatment of Sjögren’s syndrome [33–35], and gene therapeutics (pharmacological applications) directed at both upper gastrointestinal tract [5,36] and systemic [6,7,23,37] conditions. Additionally, salivary gland gene delivery has been useful for asking biological questions in vivo [38–41], as well as for creating novel models of disease [42,43].…”

Plasmid DNA is internalized from the apical plasma membrane of the salivary gland epithelium in live animals

“…First, the epithelium of these organs can be easily accessed from the oral cavity in a non-invasive fashion, by introducing fine polyethylene tubing into the major excretory ducts (Wharton’s duct in the submandibular glands and Stensen’s duct in the parotid glands). This route, that has been utilized to selectively deliver various molecules into the ductal system, has been extensively characterized for both viral- and non viral-mediated gene transfer both in animals and in humans (Adriaansen et al, 2008; Adriaansen et al, 2011; Adriaansen et al, 2010; Baccaglini et al, 2001; Baum et al, 2006; Delporte et al, 1997; Gao et al, 2011; Goldfine et al, 1997; Honigman et al, 2001; Niedzinski et al, 2003a; Niedzinski et al, 2003b; Perez et al, 2011; Samuni et al, 2008; Xu et al, 2010; Zheng and Baum, 2011; Zheng and Baum, 2005; Zheng et al, 2011a; Zheng et al, 2006; Zheng et al, 2011b; Zheng et al, 2011c). Second, we have shown that salivary glands are ideal organs to perform intravital microscopy, which enables imaging various biological processes in live animals (Masedunskas et al, 2012; Masedunskas et al, 2011; Masedunskas and Weigert, 2008; Sramkova et al, 2009; Weigert et al, 2010).…”

Sustained Exendin-4 Secretion through Gene Therapy Targeting Salivary Glands in Two Different Rodent Models of Obesity/Type 2 Diabetes

“…It has been previously reported that SGs are able to produce pharmacological levels of growth hormone and parathyroid hormone following transduction with recombinant viral vectors [30], [31]. A phase I clinical trial targeting gene transfer to the salivary glands for treating radiation induced xerostomia was initiated and a total of 11 patients have been treated with all reporting tolerance of the vector and procedure [32].…”