Endocrine Abstracts

Background: Teriparatide PTH(1-34) is an osteoanabolic agent used in the treatment of osteoporosis. Measurement of PTH(1-34) can be useful in osteoporosis treatment and in the diagnosis of pseudohypoparathyroidism (PHP) by confirming administration of PTH(1-34)

Aims: 1) To assess PTH(1-34) profiles obtained using standard Forsteo treatment compared to using a novel oral administration. 2) To confirm the PTH(1-34) in a PHP patient receiving PTH(1-34) as part of an Ellsworth Howard Test (EHT). 3) To perform a method comparison of oxidised/non oxidised forms of PTH(1-34) detected by LC-MS/MS with immunoassay.

Methods: Using a LC-MS/MS method, PTH(1-34) was measured in Pharmacokinetic (PK) profiles from a human double blinded study. Participants were given teriparatide either by a single SC injection (Forsteo,20 μg) (n=6); or in an oral dose of 0.69 mg (n=4), or 2.07mg (n=6) (EnteraBio). In an EHT, PTH(1-34), urinary PO4, and urine/plasma cyclic adenosine 3′5′-monophosphate (cAMP) were measured on samples before/after 20 μg Forsteo injection. Oxidised/non-oxidised forms of PTH(1-34) (n=390) measured by LC-MS/MS were compared against immunoassay (IDS; Boldon, UK).

Results: PK profiles showed rapid absorption of PTH(1-34) in plasma. The 2.07 mg oral dose achieved C_max of 271 pg/mL comparable to that of 20 μg Forsteo, but the injection form showed slower rate of plasma clearance (T½_(injection)=37.7min, T½_(oral)=12.5min). The EHT profile from a PHP patient showed a lack of cAMP response despite significant increase in plasma PTH(1-34) concentration. Method comparison showed LC-MS/MS results were correlated (r²=0.950), but biased (−35.5%) against the immunoassay. The bias was caused partly by a matrix effect (14.6±18.4%), cross reactivity of the immunoassay with PTH(1-84) (7.1±0.45%) and to oxidised forms of PTH(1-34) (23.9±6.1%).

Conclusion: Our LC-MS/MS method for PTH(1-34) can help validate the therapeutic use of osteoanabolic agents; confirm the lack of response to exogenous stimulation in EHT; and may explain the differences in responses to treatment due to oxidation of PTH(1-34).