Physiology Modifiers in Joint Disease Reviewed (AAEP 2011)

One researcher presented a discussion of the mechanisms and effects of some of the most commonly used physiology modifiers–hyaluronan, polysulfated glycosaminoglycans, and bisphosphonates–in equine joint disease treatment.
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Drugs are known to help cure certain ailments, but we don't often consider how exactly they promote healing when administered to horses. Physiology modifiers (drugs that are either present naturally within the body or that mimic chemicals reacting within the body), in particular, influence the cells within the musculoskeletal system. At the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas, Chris E. Kawcak, DVM, PhD, Dipl. ACVS, ACVSMR (Veterinary Sports Medicine and Rehabilitation), of Colorado State University, presented a discussion of the mechanisms and effects of some of the most commonly used physiology modifiers–hyaluronan, polysulfated glycosaminoglycans, and bisphosphonates–in equine joint disease treatment.

Hyaluronan Kawcak began the presentation discussing hyaluronan. This chemical, found within the body, interacts with the CD44 receptor, which mediates cell-cell and cell-matrix interactions "to modulate cell proliferation, migration, and gene expression." Study results indicate this interaction might influence variabilityspecifically, that the mass (molecular weight, MW) of hyaluronan administered within a joint might alter its effects. For instance, most studies show that high MW hyaluronan decreases inflammation when it binds to CD44, yet low and medium density hyaluronan might actually increase inflammation.

According to Kawcak, researchers have also shown that administering intra-articular hyaluronan can decrease pain and have disease-modifying effects such as decreased cartilage fibrillation (the softening and grooving of joint surface cartilage) within the joint. Veterinarians have used hyaluronan primarily in combination with corticosteroids in the joint. Intravenously administered hyaluronan has produced symptom-modifying effects. A study of oral preparation of hyaluronan in yearlings with hock osteochondritis dissecans resulted in decreased joint effusion (swelling).

Polysulfated glycosaminoglycans (PSGAGs) In laboratory conditions (in vitro) PSGAGs stimulate proteoglycan and collagen synthesis and decrease prostaglandin E2 (an inflammatory mediator) production. However, in vivo (in the animal) effects have been variable: In a study of an osteochondral defect model of the middle carpal (knee) joint, PSGAGs had no effect relative to the controls, while in another study using a carpal chip model of osteoarthritis (OA) PSGAGs decreased synovial effusion, subintimal fibrosis, and synovial membrane vascularity (all indicators of synovial inflammation)

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Written by:

Christy Corp-Minamiji, DVM, practices large animal medicine in Northern California, with particular interests in equine wound management and geriatric equine care. She and her husband have three children, and she writes fiction and creative nonfiction in her spare time.

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