Hibernating Bears (Ursidae)

Metabolic Magicians of Definite Interest for the Nephrologist

Peter Stenvinkel; Alkesh H Jani; Richard J Johnson

Disclosures

Kidney Int. 2013;83(2):207-212. 

In This Article

Abstract and Introduction

Abstract

Muscle loss, osteoporosis, and vascular disease are common in subjects with reduced renal function. Despite intensive research of the underlying risk factors and mechanisms driving these phenotypes, we still lack effective treatment strategies for this underserved patient group. Thus, new approaches are needed to identify effective treatments. We believe that nephrologists could learn much from biomimicry; i.e., studies of nature's models to solve complicated physiological problems and then imitate these fascinating solutions to develop novel interventions. The hibernating bear (Ursidae) should be of specific interest to the nephrologist as they ingest no food or water for months, remaining anuric and immobile, only to awaken with low blood urea nitrogen levels, healthy lean body mass, strong bones, and without evidence for thrombotic complications. Identifying the mechanisms by which bears prevent the development of azotemia, sarcopenia, osteoporosis, and atherosclerosis despite being inactive and anuric could lead to novel interventions for both prevention and treatment of patients with chronic kidney disease.

Introduction

Imagine being consulted for a 200-kg individual who has been immobilized for 5 months without food and water, all the time being anuric. After carefully collecting a blood sample, you are surprised to see that despite the subject having a 70% reduction in glomerular filtration rate (GFR) the blood urea nitrogen level is in the low normal range, and electrolytes are completely normal. If the creature would fit into the DEXA scanner, you would be surprised to find that it also has normal bone mineral density. As you begin the examination, the beast suddenly awakens and stands up, towering over you, obstreperous and aggressive, with strong muscles, bones, and teeth. If you have time to think while you rapidly exit from the den, you might ask yourself what the bear—a true 'metabolic marvel'[1]—can teach nephrologists.

Throughout the evolution of life, nature has gone through a process of trial and error to aid the survival of organisms, even under extraordinary circumstances; i.e., nature has learned what really works. 'Biomimicry' is the science that takes inspiration from unique designs and processes in nature to solve human problems.[2] We believe that by studying ingenious solutions created by nature nephrologists can learn much. Also, it seems more logical to instead of studying artifical disease models created by man in mice and rat identify animals that already learned to avoid disease during evolution. Bears figure prominently in the mythology of most native American tribes in which the bear is considered not only symbols of strength and wisdom but also a 'medicine' with impressive magical powers. Thus, the bear has a major role in many of native Americans religious ceremonies. Here, we review the remarkable ability of bears (the American black bear, Ursus americanos; the brown bear, Ursus arctos; and the grizzly bear, Ursus arctos horribilis) to protect themselves from renal failure, muscle wasting, vascular disease, and osteoporosis during hibernation despite prolonged inactivity and anuria (Figure 1). Studies of bear physiology and metabolism may provide new therapeutic directions for the treatment of human renal disease and its complications (Table 1).

Figure 1.

This black bear (Ursus americanus) depicted in the Alaskan wilderness (Redoubt Bay) is a true metabolic magician that, despite prolonged immobilization and anuria during 5–6 months of hibernation, has developed unique mechanisms to heal wounds and prevent muscle wasting, bone loss, and atherosclerosis. Comparative physiology studies (i.e., biomimicry) of hibernating bears could lead to novel treatment strategies for patients with chronic kidney disease.

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