Original Article Mitochondrial DNA Deletion Associated Oxidative Stress and Severe Male Osteoporosis S. S. Varanasi 1 , R. M. Francis 2 , C. E. M. Berger 1 , S. S. Papiha 3 and H. K. Datta 1 1 Department of Clinical Biochemistry, 2 Department of Medicine (Geriatrics) and 3 Department of Human Genetics, University of Newcastle, Newcastle-upon-Tyne, UK Abstract. We have screened the mitochondrial genome of 15 men with symptomatic vertebral fractures (median age 62 years, range 27–72 years) and 17 male control subjects (median age 61 years, range 40–73 years) for the presence of mitochondrial DNA (mtDNA) deletions in peripheral monocyte DNA. Polymerase chain reaction analysis provided evidence of a common age-related (4.9 kb) mtDNA deletion situated between nucleotides 8470 and 13.460 of the genomic sequence in 5 of the 17 controls (29%) and 9 of the 15 patients (60%) investigated. Southern blotting and polymerase chain reaction revealed a novel 3.7 kb deletion in 2 patients. One of the affected patients, a 27-year-old man with severe osteoporosis (lumbar spine bone mineral density (BMD) 0.381 g/cm 2 ; Z-score 76.45) was found to harbor deletion in almost 50% of the mitochondria. The patient had a blood lactic acid level (4.6 nM) that was over 3 times the upper reference range (0–1.3 mM), thus confirming the presence of systemic oxidative stress. Further analysis by modified primer shift polymerase chain reaction showed the 5' breakpoint to be between the nucleotides 10.63 kb and 10.80 kb of the mtDNA. The second patient harboring the 3.7 kb deletion was older (62 years) with less severe osteoporosis (lumbar spine BMD 0.727/cm 2 ; Z-score 72.58) and the proportion of affected mitochondria was lower (25%). The significance of these findings is discussed and the possible relation between oxidative stress and acceler- ated bone loss is examined. Keywords: Lactic acidosis; Mitochondrial DNA; Osteoporosis; Oxidative stress Introduction The maintenance of bone mass is influenced by genetic, hormonal, mechanical and nutritional factors, which modulate the local and systemic mechanisms regulating bone turnover. A variety of local and circulating hormones, cytokines and intermediary metabolites may influence the number and activity of bone-forming osteoblasts and bone-resorbing osteoclasts. Disruption of the close coupling between bone resorption and formation may lead to bone loss and the development of osteoporosis. The role of metabolic acidosis in the bone loss and the development of osteoporosis, although somewhat neglected and under-investigated, is never- theless well recognized. Indeed, chronic metabolic acidosis is believed to reduce bone density by directly dissolving bone matrix, as well as by osteoblast inhibition and osteoclast stimulation [1]. The dissolution of bone by chronic metabolic acidosis may also be mediated via hypophosphatemia and altered parathyroid hormone and 1,25-dihydroxyvitamin D concentration and action [2]. The stimulation of bone resorption is far less intense when the pH is lowered by raising the level of carbonic acid following carbon dioxide retention, seen in respiratory acidosis [3]. These observations have led to suggestions that the retention of even a small proportion of acid generated from the metabolism of an ordinary omnivore diet might contribute to the Osteoporos Int (1999) 10:143–149 ß 1999 International Osteoporosis Foundation and National Osteoporosis Foundation Osteoporosis International Correspondence and offprint requests to: Dr H. K. Datta MB, BS, PhD, Department of Clinical Biochemistry, The Medical School, University of Newcastle, Newcastle-upon-Tyne NE2 4HH, UK. Tel +44 (0)191 222 6759. Fax: +44 (0)191 222 6227. e-mail: h.k.datta@newcastle.ac.uk