John Leonora is notable for his research into the critical role of hypothalamic "factors" for indirectly controlling the metabolism of such avascular tissues as the dental enamel, the dentin, and the Islands of Langerhans (pancreas). His contributions have given a radically new perspective to the systemic role of the brain in both health and disease. Most of his research was carried out during his 45 years as a faculty member at Loma Linda University

Loma Linda University

Loma Linda University is a Seventh-day Adventist coeducational health sciences university located in Loma Linda, California, United States. The University comprises eight schools and the Faculty of Graduate Studies...

 and instructor at the university's predecessor, the College of Medical Evangelists.

Biographical Information

John Leonora, the son of Joseph Leonora (March 14, 1883 - November 20, 1942) and Carmela Folise Leonora (April 29, 1888-June 20, 1965), was born in Milwaukee, Wisconsin

Milwaukee, Wisconsin

Milwaukee is the largest city in the U.S. state of Wisconsin, the 28th most populous city in the United States and 39th most populous region in the United States. It is the county seat of Milwaukee County and is located on the southwestern shore of Lake Michigan. According to 2010 census data, the...

, soon after his parents arrived as immigrants from Sicily

Sicily

Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...

. They had left their eldest daughter in the Sicilian province of Enna where she had already grown to adulthood, married and had children. Their second daughter had died of influenza in Sicily near the end of World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

.

After Joseph Leonora died in 1942, Carmela Leonora found employment as a hand stitcher in an Italian shoe factory. John became an errand boy for various businesses throughout Milwaukee. At the same time he excelled in school and became a proficient pianist, accompanying and playing in jazz combos. He was an active member of the Italian club at Lincoln High School. Because of excellent grades he was awarded a one-year scholarship at the University of Wisconsin–Milwaukee.

Upon receiving his B.S. degree at the University of Wisconsin–Madison

University of Wisconsin–Madison

The University of Wisconsin–Madison is a public research university located in Madison, Wisconsin, United States. Founded in 1848, UW–Madison is the flagship campus of the University of Wisconsin System. It became a land-grant institution in 1866...

, John took an interim position as a laboratory assistant in chemistry and obtained teaching credentials at what is now Andrews University

Andrews University

Andrews University is a Seventh-day Adventist university in Berrien Springs, Michigan, United States. Founded in 1874 as Battle Creek College in Battle Creek, Michigan, it was the first higher education facility started by Seventh-day Adventists, and is the flagship university of the Seventh-day...

, Berrien Springs, Michigan

Berrien Springs, Michigan

Berrien Springs is a village in Berrien County in the U.S. state of Michigan. The population was 1,862 at the 2000 census. The village is located within Oronoko Charter Township. Berrien Springs is best known for its Seventh-day Adventist community and Andrews University...

. There he met Johanna Mae Zwemer, who was working toward a secretarial degree. They later married in 1952. Meanwhile Leonora had returned to Madison and the University of Wisconsin. There he and his wife lived while he completed his Ph.D., obtained a federal fellowship, and embarked on his career as an endocrinologist.

For more than four decades, Dr. Leonora was active in his chosen field of medical physiology. He not only mentored numerous graduate students, but provided leadership for research conducted in his own laboratory. In his research he demonstrated surgical skills on animals as diverse as a 200 pound pig or a mouse weighing only a few ounces. He also delighted in teaching. His lectures were remembered by his students for their clarity and quiet humor.

John was profoundly dedicated to his family—his wife, Johanna, daughters Carmela and Andrea, and three grandchildren. In his leisure time he delighted in the quietude of his country home. He spent hours working in the yard and cooking in the kitchen. He was famous for his homemade pizza, pasta sauce, and biscotti.

Dr. Leonora’s compassion, his career and his contributions will never be forgotten. He literally opened the portal to a new, dynamic, interactive view of the brain’s function in disease, in health, and in life itself.

Education

1949: B.S. in Zoology and Chemistry, University of Wisconsin, Madison, WI

1954: M.S. in Zoology, University of Wisconsin, Madison, WI

1957: Ph.D. in Endocrinology, University of Wisconsin, Madison, WI

Title of Dissertation: Separation and Purification of Follicle Stimulating and Luteinizing Hormone from Ovine Pituitary Glands

1957-59: NIH Postdoctoral Fellow, University of Wisconsin, Madison, WI

Academic Appointments

1952-1957: Research Assistant, Department of Zoology and Endocrinology, University of Wisconsin, Madison, WI

1959-1963: Instructor, Department of Medicine, College of Medical Evangelists, Los Angeles, CA

1963-1968: Assistant Professor, Department of Physiology, Loma Linda University

Loma Linda University

Loma Linda University is a Seventh-day Adventist coeducational health sciences university located in Loma Linda, California, United States. The University comprises eight schools and the Faculty of Graduate Studies...

, Loma Linda, CA

1968-1970: Associate Professor, Department of Physiology, Loma Linda University

1970-2002: Professor and Co-Chairman, Department of Physiology and Pharmacology, Loma Linda University

Lectures

School of Medicine:

• Fluid and Electrolyte Homeostasis
• Endocrine Physiology

School of Dentistry:

• Systemic Factors in Dental Health
• Calcium Homeostasis
• Hormonal Factors in Dental Health

Graduate School:

• Hormonal Control of Nutrient Homeostasis

Committee Memberships

• Member, Executive Committee, School of Medicine
• Member, Graduate School Council
• Member, Scholarship Committee, Graduate School

Invited Lectures and Symposia

• Systemic effects of sugar on the hypothalamic-parotid gland endocrine axis. Alumni Postgraduate Convention, Loma Linda University, February 1974.

• Systemic effects of sugar on the hypothalamic-parotid gland endocrine axis. Dietetics Convention, School of Health, Loma Linda University, 1974.

• Role of systemic resistance as mediated by hormone action in controlling the incidence of dental caries. Alumni Postgraduate Convention, School of Medicine, Loma Linda University, March 1975.

• Role of trace elements in glucose metabolism, Southern California Nutrition Society, Fullerton, CA, March 1978.

• Physiological observations of a new parotid hormone. The Endocrine Society, Washington, D.C., June 1980.

• Role of hormones in cariostasis. Continuing education lecture, School of Dentistry, Loma Linda University, April 1981.

• New concepts in dental caries. Second Annual Nutrition Symposium, Loma Linda University, May 1983.

• Physiologic significance of the hypothalamic-parotid gland endocrine axis as it relates to dental health. Weimar Institute, Weimar, CA, May 1988.

Academic Awards

1976: Walter E. Macpherson Society, Research Award

1980: Walter E. Macpherson Society, Basic Science Teacher Award

1980: Sigma Xi Research Merit Award

1988: Walter E. Macpherson Society Basic Science Teacher Award

1988: Sigma Xi Research Merit Award

2005: Honorary Omicron Kappa Upsilon Award by the Chi Chi Chapter, Loma Linda University.

Research Grant Awards

In 40 years of active investigation, John Leonora received over one million dollars in research grant awards from such entities as the National Institutes of Health, the Walter E. Macpherson Society, the Don Baxter Foundation, the Pediatric Research Endowment Fund and the Basic Science Research Fund.

Research Contributions

Gonadotropic hormones. Based on his doctoral studies and subsequent research fellowship, John Leonora initially intended to devote his career to the investigation of gonadotropic hormones.

Dentinal fluid transport. One day he received a telephone call from Dr. Ralph R. Steinman, a dental colleague, who had been studying the flow of dentinal fluid in rats from the odontoblasts in the dental pulp through the dentin using an intraperitoneal injection of the fluorescent dye, acriflavine hydrochloride. He found that in the teeth of rats fed a cariogenic diet the flow of dentinal fluid was markedly reduced. He wondered if some systemic mechanism was involved in this impairment and so decided to contact Dr. John Leonora, as an endocrinologist.

Hypothalamus

Hypothalamus

The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...

. This was the beginning of a decades-long collaborative journey. John Leonora first suggested that none of the recognized hormones were plausible candidates for regulating dentinal flow transport (DFT), but that the hypothalamus might well be an alternative hormonal source. Quickly they found that infusing rats with a crude extract from rabbit hypothalami triggered increased DFT activity. This, however, raised the question whether the hypothalamic factor had a direct effect on the teeth or rather had an indirect effect characteristic of other hypothalamic hormones.

Parotid hormone. Assuming that the hypothalamic factor was mediated through one of the major salivary glands, they found that this factor was biologically active when administered to rats with intact parotid gland

Parotid gland

The paired parotid glands are the largest of the salivary glands. They are each found wrapped around the mandibular ramus, and secrete saliva through Stensen's ducts into the oral cavity, to facilitate mastication and swallowing and to begin the digestion of starches.-Location:The parotid glands...

s but was wholly ineffective in rats that had the parotid glands removed. There was no involvement of the other salivary glands. They concluded that the direct regulation of DFT was therefore secreted by the parotid glands and this endocrine function was controlled by the hypothalamus.

Purification of the hormones. The next step was to isolate the purified parotid hormone from porcine glands, determine its amino acid structure and then confirm its stimulation of DFT. Then the hypothalamic parotid hormone releasing factor was partially purified but not completed because of the rejection of a research grant application. While the research was thus diverted it persisted in other directions.

Antibody to the parotid hormone. First, an antibody to the porcine parotid hormone was produced, isolated and used for a radio-immunoassay of the parotid hormone. Later an ELISA method (enzyme linked immunoadsorbent assay) was developed for measuring the parotid hormone titer in biological fluids.

Suppressive effect of sucrose. Then the research focused on the mechanism by which dietary sucrose suppressed the DFT. Initial studies suggested that the sucrose suppressed the secretion of the parotid hormone. Further studies, however, showed that the sucrose effect occurred indirectly by inhibiting secretion of the hypothalamic parotid hormone releasing factor. Then it was found that the sucrose effect could be effectively reversed by the infusion of the compound carbamyl phosphate through the internal carotid artery. This confirmed that the site of action was within the central nervous system—namely the hypothalamus.

Effect of carbamyl phosphate. Not surprisingly, intact rats fed carbamyl phosphate along with a cariogenic diet showed a highly significant reduction in caries. Carbamyl phosphate, however, was ineffective in parotidectomized rats. Therefore, an intact hypothalamic-parotid gland endocrine axis was found to be necessary for the effectiveness of carbamyl phosphate.

Neural stimuli of the hypothalamus

Hypothalamus

The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...

. The next question was, what physiological factors normally stimulate the secretion of the parotid hormone? Feeding pigs a standard pig chow proved to effectively stimulate parotid hormone secretion along with the copious secretion of saliva. Surprisingly, pigs fed nonnutritive substances and exposed to auditory, olfactory and visual cues salivated profusely but these cues did not change the fasting level of the parotid hormone. This demonstrated that, although the endocrine and exocrine functions of the parotid glands occur concurrently, they must be controlled by different mechanisms. The nutritive composition thus proved to be critical for the secretion of the parotid hormone. Apparently nutritive substrates activate neural stimuli going to the hypothalamus, which in turn activates the hypothalamic-parotid gland endocrine axis that then stimulates the dentinal fluid transport mechanism.

Formation of dentin

Dentin

Dentine is a calcified tissue of the body, and along with enamel, cementum, and pulp is one of the four major components of teeth. Usually, it is covered by enamel on the crown and cementum on the root and surrounds the entire pulp...

. At this critical juncture a group of investigators at the University of Oulu Dental School, Oulu, Finland (Tjaderhane, L. et al., (1994) discovered that the parotid hormone not only regulates the flow of dentinal fluid but also is involved in the formation of dentin—dentinogenesis. They also found that a high sucrose diet in young rats suppressed primary dentinogenesis. The injection of carbamyl phosphate significantly reversed the effect of sucrose—but only in intact rats. Furthermore, carbamyl phosphate prevented the atrophy of the parotid glands associated with the ingestion of sucrose.

Synthesis of the parotid hormone. Subsequent research successfully cloned the porcine cDNAs that code for the parotid hormone gene. The amino acids encoded by these cDNAs agreed with the amino acid sequence of the hormone isolated from the porcine parotid glands. In addition, a commercially available synthetic parotid hormone was found to have an activity indistinguishable from the isolated parotid hormone or the gene-expressed hormone.

Acinar cell source of the parotid hormone. Meanwhile, it was discovered that the acinar cells of the parotid glands are apparently the source of the parotid hormone.

Regulation of insulin

Insulin

Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....

secretion. Finally, preliminary research suggested the parotid hormone not only regulates dental structures but also influences insulin secretion by the pancreas.

Other tissues/organs. These systemic effects have yet to be followed up but may well include other glandular and/or avascular tissues. As Dr. Leonora stated in an undated letter, “I anticipate finding receptors [for the parotid hormone] in the odontoblasts in teeth, osteocytes in bone matrix, Islets of Langerhans. . . .”

Published Research

1. Leonora, J., McShan, W. H. & Meyer, R. K. (1956). Factors affecting extraction and recovery of follicle stimulating hormone from sheep pituitary glands. Proceedings of the Society for Experimental Biology and Medicine (92) 524-529.
2. Leonora, J., McShan, W. H., & Meyer, R. K. (1958). Separation of a luteinizing hormone fraction from sheep pituitary glands by use of ion exchange resin. Endocrinology (63) 867-888.
3. Meyer, R. K., Leonora, J., & McShan, W. H. (1959). Effectiveness of sheep FSH and LH preparations on spermiation in the frog. In A. Albert (Ed.), Human pituitary gonadotropins, pp. 326–328. Springfield, IL: Charles C. Thomas.
4. Meyer, R. K., Leonora, J., & McShan, W. H. (1959). Response of ovary, prostate and testes to human and sheep gonadotroic preparations. Effectiveness of human and sheep gonadotropic preparations on ovulation in immature rats. In A. Albert (Ed.), Human pituitary gonadotropins, pp. 329–334. Springfield, IL: Charles C Thomas.
5. Meyer, R. K., Leonora, J., & McShan, W. H. (1959). Effectiveness of human and sheep gonadotropic preparations on ovulation in immature rats. In A. Albert (Ed.), Human pituitary gonadotropins (pp. 335–338). Springfield, IL: Charles C Thomas.
6. Leonora, J., and Steinman, R. R. (1968). Evidence suggesting the existence of a hypothalamic parotid gland endocrine axis. Endocrinology (83). 807-815.
7. Steinman, R. R. and Leonora, J. (1969). Suppression of dental caries by chemical activation of the hypothalamic-parotid endocrine axis. Journal of Dental Research (48) S207, Abstr #666.
8. Sanchez, A., Steinman, R. R., & Leonora, J. (1970). Effect of diet on dentinal fluid movement in germfree and nongermfree rats. American Journal of Clinical Nutrition (23) 686-690.
9. Steinman, R. R., and Leonora, J. (1971). Relation between early changes in dentin and later dental caries. Journal of Dental Research (50)247, Abstr #780.
10. Steinman, R. R. and Leonora, J. (1971). Relationship of fluid transport through the dentin to the incidence of dental caries. Journal of Dental Research (50)6, Part 2:1536-1543.
11. Steinman, R. R., Leonora, J., Shiroma, E., & Dwyer, T. (1975). Lactic acid concentration in various tooth structures in rats maintained on either a cariogenic or noncariogenic diet. Journal of Dental Research (54)2. 419, Abstr.
12. Steinman, R. R., & Leonora, J. (1975). Effect of infusing selected chemical compounds on dentinal fluid movement in the rat. Journal of Dental Research (54)3. 567-569.
13. Steinman, R. R., & Leonora, J. (1975). Effect of selected dietary additives on the incidence of dental caries in the rat. Journal of Dental Research (54)3. 570-577.
14. Steinman, R. R., & Leonora, J. (1975). Acidogenic potential of cariogenic and noncariogenic diets in the rat. Journal of Dental Research (54)3. 578-580.
15. Steinman, R. R., & Leonora, J. (1977). Physiologic resistance to dental caries. Journal of the Missouri Dental Association (57)3. 14-21.
16. Steinman, R. R. & Leonora, J. & Tieche, J. M. (1979). Susceptibility to dental caries. Australian Dental Journal (24)4. 222-224.
17. Steinman, R. R., Leonora, J., & Singh, R. J. (1980). The effect of desalivation upon pulpal function and dental caries in rats. Journal of Dental Research (59)2. 176-185.
18. Tieche, J. M., Leonora, J., & Steinman, R. R. (1980). Isolation and partial characterization of a porcine parotid hormone that stimulates dentinal fluid transport. Endocrinology (106). 1994-2005.
19. Steinman, R. R. and Leonora, J. & Tieche, J. M. (1980). Susceptibility to dental caries: The pulp plays a major role. [Oral Health] (70). 43.
20. Tieche, J. M., Leonora, J., Berk, L. S., & Steinman, R. R. (1981). A radioimmunoassay procedure for quantitating parotid hormone. Biochemical and Biophysical Research Communications (98). 154-162.
21. Leonora, J., & Steinman, R. R. DFT: Its cariostatic effect. Teaching syllabus, 1981.
22. Leonora, J., Tieche, J. M., & Celestin, J. (1987). Physiological factors affecting the secretion of parotid hormone. American Journal of Endocrinology - Endocrinology and Metabolism (252). E477-E484.
23. Leonora, J. Tieche, J. M., and Cook, D. S. (1988). Evidence for the insulinotropic effect from rat parotid glands. Diabetes (37). 441-445.
24. Tieche, J. M., & Leonora, J. Biological and chemical evidence for the existence of a porcine hypothalamic parotid hormone-releasing factor. (1989). Biochemical and Biophysical Research Communications (159)3. 899-906.
25. Leonora, J., Tieche, J. M., & Steinman, R. R. (1992). The effect of dietary factors on intradentinal dye penetration in the rat. Archives of Oral Biology (37). 733-741.
26. Leonora, J., Tieche, J.M., & Steinman, R. R. (1993). Stimulation of intradentinal dye penetration by feeding in the rat. Archives of Oral Biology (38). 763-767.
27. Leonora, J. Tieche, J. M., & Steinman, R. R. (1993). Further evidence for a hypothalamus-parotid gland endocrine axis in the rat. Archives of Oral Biology (38). 911-916.
28. Tieche, J. M., Leonora, J. & Steinman, R. R. (1994). High-sucrose diet inhibits basal secretion of intradentinal dye penetration-stimulating parotid hormone in pigs. Journal of Applied Physiology (76). 218-222.
29. Tieche, J. M., & Leonora, J. (1995). Acute secretion of immunoreactive parotid hormone in response to different diets in the pig. Archives of Oral Biology (40)6. 559-565.
30. Leonora, J., Tjaderhane, L., & Tieche, J. M. Parotid (2002). Gland function and dentin apposition in rat molars. Journal of Dental Research (81)4. 259-264.
31. Leonora, J., Tjaderhane, L. and Tieche, J.M. (2002). Effect of dietary carbamyl phosphate on dentin apposition in rat molars. Archives of Oral Biology (47). 147-153.
32. Zhang, Q., Szalay, A. A., Tieche, J. M. Kyeyune-Nyombi, E., Sands, J. F., Oberg, K. C. and Leonora, J. (June 2005). Cloning and functional study of porcine parotid hormone, a novel proline-rich protein. Journal of Biological Chemistry (280)23. 22233-22244.

Research Abstracts

1. Leonora, J. and Steinman, R. R. Physiological observations of a new parotid hormone (PH). Proc. Inter. Union Physiol. Soc. (The Endocrine Society), Abstr. #781. Washington, DC., 1980.
2. Crane, M. G. and Leonora, J. Effects of medroxyprogesterone acetate and other steroids in combination with high sodium intake. Clin. Res. 18:167, 1970.
3. Leonora, J., and Crane, M. G. Effects of long-term administration of medroxyprogesterone acetate and other estrogens in the rat. Clin. Res. 18:169, 1970.
4. Wright, K. R., Weller, S. E., McMillan, P. J., Tieche, J. M., and Leonora, J. Sucrose-induced decrease in bone specific gravity in growing rats is inhibited by carbamyl phosphate. British Association of Clinical Anatomists with the American Association of Clinical Anatomists (3rd joint meeting), Cambridge, England, July 2000.

External links

For further information, please see Clyde Roggenkamp (ed.) "Dentinal Fluid Transport". Loma Linda, CA: Loma Linda University Press, 2004.