Pentosidine in osteoarthritis: HPLC determination in body fluids and in tissues

Total serum pentosidine quantification using liquid chromatography-tandem mass spectrometry

Pentosidine (PEN) is an Advanced Glycation End-product (AGE) that is known to accumulate in bone collagen with aging and contribute to fracture risk. The PEN content in bone is correlated with serum PEN, making it an attractive, potential osteoporosis biomarker. We sought to develop a method for quantifying PEN in stored serum. After conducting a systematic narrative review of PEN quantification methodologies, we developed a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for quantifying total serum PEN. Our method is both sensitive and precise (LOD 2 nM, LOQ 5 nM, %CV < 6.5 % and recovery 91.2-100.7 %). Our method is also equivalent or better than other methods identified in our review. Additionally, LC-MS/MS avoids the pitfalls and limitations of using fluorescence as a means of detection and could be adapted to investigate a broad range of AGE compounds.

Possible role of methylglyoxal and glyoxalase in arthritis

OA (osteoarthritis) and RA (rheumatoid arthritis) lead to deterioration of the joints. Early OA is associated with loss of bone due to increased bone remodelling. A role for inflammation is thought to be integral to the pathology. RA is a chronic inflammatory disease of the synovium, a membrane lining the non-weight-bearing surfaces of the joint. The mainstay of RA diagnostic testing is for autoantibodies. Rheumatoid factor has been a primary diagnostic test; however, sensitivity is approximately 75%, but specificity is limited. Recently, detection of antibodies against cyclic citrullinated peptide, identified as a screening marker and marker of disease progression, has been proposed. Studies of glycation in arthritis have focused mostly on levels of AGEs (advanced glycation end-products), Nε-carboxymethyl-lysine and pentosidine. There was a weak correlation of skin and urinary pentosidine with joint damage in early-stage OA. RAGE (receptor for AGEs) is a cell-surface receptor in the synovial tissue of patients with OA and RA. The RAGE agonist S100A12 is increased in RA and OA. Activation of RAGE may decrease expression of Glo1 (glyoxalase I). Conflict between RAGE-activated inflammatory signalling and Nrf2 (nuclear factor-erythroid 2-related factor 2) regulation of basal and inducible expression of Glo1 may be involved. Thereby glyoxal- and methylglyoxal-derived AGEs may be increased in OA and RA. Further studies are now required to investigate the role of glyoxalase and dicarbonyl glycation in OA and RA for early-stage diagnosis and potential novel preventive therapy.

Pentosidine, an advanced glycation end-product, may reflect clinical and morphological features of hand osteoarthritis

The study investigates pentosidine levels, an advanced glycation end-product, in patients with erosive and non-erosive hand osteoarthritis (HOA) and determine its potential association with clinical findings and imaging-defined joint damage.Pentosidine was measured by HPLC in serum and urine of 53 females with HOA (31 erosive and 22 non-erosive HOA) and normalised to the total serum protein or urinary creatinine, respectively. Pain, joint stiffness and disability were assessed by the Australian/Canadian OA hand index (AUSCAN). The hand radiographs scored according to the Kallman grading scale were assessed to determine a baseline value and reassessed after two years.The levels of urine pentosidine, but not of serum pentosidine, were higher in patients with erosive HOA than in non-erosive HOA (p=0.039). Urinary pentosidine correlated with CRP (r=0.302, p=0.031), ESR (r=0.288, p=0.041) and AUSCAN (r=0.408, p=0.003). Serum pentosidine, but not in urine, significantly correlated with the Kallman radiographic score in erosive HOA at the baseline (r=0.409, p=0.022) and after 2 years (r=0.385, p=0.032). However, when corrected for age and disease duration, only correlation between urine pentosidine and AUSCAN remained significant (r=0.397, p=0.004).Our data suggest that serum and urine pentosidine levels may relate to the distinctive clinical and morphological features of HOA.

In end stage osteoarthritis, cartilage tissue pentosidine levels are inversely related to parameters of cartilage damage

OBJECTIVES

Age is the most prominent predisposition for development of osteoarthritis (OA). Age-related changes of articular cartilage are likely to play a role. Advanced glycation endproducts (AGEs) accumulate in cartilage matrix with increasing age and adversely affect the biomechanical properties of the cartilage matrix and influence chondrocyte activity. In clinical studies AGEing of cartilage and its relation to actual cartilage damage can only be measured by surrogate markers (e.g., serum, skin or urine AGE levels and imaging or biochemical markers of cartilage damage). In this study actual cartilage AGE levels were directly related to actual cartilage damage by use of cartilage obtained at joint replacement surgery.

METHODS

Cartilage and urine samples were obtained from 69 patients undergoing total knee replacement. Samples were analyzed for pentosidine as marker of AGE. Cartilage damage was evaluated macroscopically, histologically, and biochemically.

RESULTS

Cartilage and urine pentosidine both increased with increasing age. The higher the macroscopic, histological, and biochemical cartilage damage the lower the cartilage pentosidine levels were. In multiple regression analysis age is not found to be a confounder.

CONCLUSION

There is an inverse relation between cartilage AGEs and actual cartilage damage in end-stage OA. This is likely due to ongoing (ineffective) increased turnover of cartilage matrix proteins even in end stage disease.

Skin and urine pentosidine weakly correlate with joint damage in a cohort of patients with early signs of osteoarthritis (CHECK)

OBJECTIVES

Age-related changes in articular cartilage are likely to play a role in the aetiology of osteoarthritis (OA). One of the major age-related changes in cartilage is the accumulation of advanced-glycation-endproducts (AGEs). Since, cartilage tissue is not readily available from patients for studying AGE levels, alternative approaches such as analyzing skin and urine are needed to study the role of cartilage AGE levels in OA.

METHODS

Paired human skin and cartilage samples were obtained post mortem. Paired skin and urine samples were obtained from the CHECK cohort (early OA patients). Pentosidine levels were measured by high-performance liquid chromatography (HPLC). As marker of cumulative cartilage damage X-rays of both knees and hips were scored. Urinary CTXII (uCTXII) levels were measured, to assess current cartilage breakdown.

RESULTS

Cartilage and skin pentosidine correlate well (R=0.473, P=0.05). Skin pentosidine was higher in mild (summed (Kellgren & Lawrence K&L) over four large joints ≥4) compared to no (summed K&L≤3) radiographic OA (P=0.007). Urinary pentosidine was not different between these two groups. Skin pentosidine levels were not related to cartilage breakdown (highest vs lowest tertile of uCTXII). Urinary pentosidine, however, was higher in the highest compared to the lowest uCTXII tertile (P=0.009). Multiple regression analysis showed age to be the only predictor of the summed K&L score and age, creatinine clearance and urinary pentosidine as predictors of uCTXII.

CONCLUSION

The higher skin and urinary pentosidine levels in those with mild compared to no radiographic joint damage and low vs high cartilage breakdown respectively suggest that AGEs may contribute to disease susceptibility and/or progression. However, relations are weak and cannot be used as surrogate markers of severity of OA.

Biomarkers in the development of novel disease-modifying therapies for osteoarthritis

Identification and utilization of biomarkers is vitally important for the successful development of disease-modifying osteoarthritis drugs. Biochemical and imaging platforms hold great promise to deliver such biomarkers. Studies indicate a marked increase in biochemical products arising from the breakdown and biosynthesis of collagen, extracellular matrix and bone in osteoarthritis. These molecules have been associated with disease severity and may also have prognostic value as indicators of disease progression. However, issues including biological variability and lack of tissue specificity currently hinder the utility of these molecular markers in drug development. Imaging technologies hold great potential for sensitive and accurate measurement of disease-related structural damage. Drawbacks, including expense, need for validation and limited accessibility also limit the utility of these technologies. In this article, the potential value and challenges in developing and utilizing biomarkers in disease-modifying osteoarthritis drug development will be discussed.