High-Dose Biotin, an Inducer of Glucokinase Expression, May Synergize with Chromium Picolinate to Enable for Type II Disbetes

Medical Hypotheses (1999) 52(5), 401Ð406 © 1999 Harcourt Brace & Co. Ltd Article No. mehy.1997.0682 High-dose biotin, an inducer of glucokinase expression, may synergize with chromium picolinate to enable a definitive nutritional therapy for type II diabetes

M. F. McCarty

NutriGuard Research, Encinitas, CA, USA

Summary Glucokinase (GK), expressed in hepatocyte and pancreatic β cells, has a central regulatory role in glucose metabolism. Efficient GK activity is required for normal glucose-stimulated insulin secretion, postprandial hepatic glucose uptake, and the appropriate suppression of hepatic glucose output and gluconeogenesis by elevated plasma glucose. Hepatic GK activity is subnormal in diabetes, and GK may also be decreased in the β cells of type II diabetics. In supraphysiological concentrations, biotin promotes the transcription and translation of the GK gene in hepatocytes; this effect appears to be mediated by activation of soluble guanylate cyclase. More recent evidence indicates that biotin likewise increases GK activity in islet cells. On the other hand, high-dose biotin suppresses hepatocyte transcription of phosphoenolpyruvate carboxykinase, the rate-limiting enzyme for gluconeogenesis. Administration of high-dose biotin has improved glycemic control in several diabetic animals models, and a recent Japanese clinical study concludes that biotin (3 mg t.i.d. orally) can substantially lower fasting glucose in type II diabetics, without side-effects. The recently demonstrated utility of chromium picolinate in type II diabetes appears to reflect improved peripheral insulin sensitivity Ð a parameter which is unlikely to be directly influenced by biotin. Thus, the joint administration of supranutritional doses of biotin and chromium picolinate is likely to combat insulin resistance, improve β-cell function, enhance postprandial glucose uptake by both liver and skeletal muscle, and inhibit excessive hepatic glucose production. Conceivably, this safe, convenient, nutritional regimen will constitute a definitive therapy for many type II diabetics, and may likewise be useful in the prevention and management of gestational diabetes. Biotin should also aid glycemic control in type I patients.

GLUCOKINAS: A CRUCIAL REGULATOR OF glucose concentrations, its activity is rate-limiting for the GLUCOSE METABOLISM metabolic utilization of glucose (responsible for signaling glucose-stimulated insulin release) (3–9). In hepatocytes, Glucokinase (GK) is a form of hexokinase (type IV) that GK activity is rate-limiting for postprandial glucose-6- is distinguished from other such enzymes by a high Km phosphate synthesis, and thus for glucagon synthesis (~8 mM) and by the absence of feedback inhibition by the ‘direct route’ (10,11). GK activity is also crucial by glucose-6-phosphate (1,2). It is expressed chiefly in to the feedback mechanism whereby increased plasma hepatocytes and pancreatic islets, where it is respon- glucose suppresses hepatic gluconeogenesis and net glyco- sible for a substantial portion of the glycolytic flux. In genolysis (12–15). The impact of GK on gluconeogenesis pancreatic β cells, GK is considered to be the ‘glucose is believed to be mediated by the following sequence of sensor’, since at physiological or supraphysiological events: GK catalyzes glucose-6-phosphate production at Received 2 September 1997 a rate that is roughly proportional to glucose levels, Accepted 15 October 1997 leading to an increase in fructose-6-phosphate. This latter Correspondence to: Mark F. McCarty MD, NutriGuard Research, 1051 compound gives rise to fructose-2,6-diphosphate, an Hermes Avenue, Encinitas, CA 92024, USA allosteric activator of phosphofructokinase and inhibitor

401 402 McCarty

of fructose diphosphatase. This shift in enzyme acti- decreased in type II diabetics. Reduced β-cell GK activity vation, in conjunction with the increased production of has been reported in male Zucker diabetic fatty rats fructose-6-phosphate, results in a substantial increase (35), and in Sprague–Dawley rats receiving a high-fat diet in fructose-1,6-diphosphate, a potent allosteric activator (36), but not in diabetic GK rats (37). Several rodent of pyruvate kinase (16–18). In the longer term, GK studies document decreased activity of the mitochondrial activity promotes the synthesis of pyruvate kinase; appar- glycerol-3-phosphate dehydrogenase (G3PD) in diabetic β ently glucose-6-phosphate (or some metabolite thereof) cells (35,37–39); this lesion would be expected to reduce activates transcription of this enzyme (19). The short- glucose oxidation by beta cells (as is observed), but not term and long-term activation of pyruvate kinase – an necessarily glycolytic flux. Recently, Belgian scientists enzyme which irreversibly diverts substrate from the obtained pancreatic islets from recently deceased diabetic gluconeogenic pathway – is probably the most funda- and non-diabetic subjects; this study confirmed that mental mechanism by which GK activity prevents in- G3PD activity was subnormal in diabetic islets, but unfor- appropriate gluconeogenesis when plasma glucose levels tunately GK activity was not measured (40). It is notable, are increased above normal fasting levels. (It will be of however, that total glucose utilization (i.e. flux through relevance to the subsequent discussion to note that all hexokinases) in diabetic islets was about half of that metformin’s anti-diabetic action may reflect its ability in the control islets; glucose oxidation was decreased by to activate pyruvate kinase) (20,21). 63%. The observed decrease in glucose utilization would be consistent with a reduction in GK activity. Indeed, when medium glucose concentrations were increased DEFICIENT GLUCOKINASE ACTIVITY IN from 100 mg/dl to 300 mg/dl, the increment in glucose DIABETES utilization in control islets was roughly triple that seen in In light of the fact that type II diabetes is characterized by diabetic islets; since flux through other islet hexokinases impaired β-cell insulin response to postprandial glucose would already be maximized at 100 mg/dl glucose, the levels, reduced oral glucose tolerance, and a failure of incremental flux, as glucose concentration is raised, should elevated glucose to adequately suppress gluconeogenesis, be proportional to effective GK activity. In islets from it is reasonable to speculate that reduced GK activity streptozotocin-treated diabetic rats, glucose utilization may play a role in the diabetic syndrome. Indeed, a rare is not significantly decreased despite a very substantial genetically linked early-onset form of diabetes (MODY2) reduction in G3PD activity (38); therefore, a reduction is now known to result from mutations that disrupt in this latter activity is not likely to explain the decrease the function of GK (11,22–24). In transgenic rodents, the in glucose utilization noted in diabetic human islets. Nor temporary or permanent suppression of GK expression in is a decrease in GLUT 2 expression a likely explanation liver and/or pancreas results in persistent hyperglycemia for this phenomenon (3,8,41). and glucose intolerance (4–6,25). Even if GK expression were normal in diabetic tissues, In hepatocytes, GK synthesis is stimulated by insulin, an up-regulation of its expression could be expected and dominantly repressed by glucagon (or other measures to have favorable effects on glycemic control. Indeed, that raise hepatocyte cAMP levels) (19,26–28). Insulin transgenic mice with extra copies of GK in their genomes activity on hepatocytes tends to be subnormal in both tend to be hypoglycemic relative to controls (10,25). In types of diabetes, in type II patients, this reflects hepato- transgenic mice expressing increased levels of c-Myc cyte insulin resistance mediated by excessive portal free in their livers – which results in enhanced hepatic GK fatty acids (29). Glucagon production is typically elevated production – streptozotocin treatment has a less dramatic in type I patients, and in many with type II disease, either hyperglycemic impact (33). Thus, measures which could absolutely or relative to the prevalent hyperglycemia (30). safely elevate expression of GK in hepatocytes and/or It thus may be predicted that hepatic GK activity will β cells could be expected to be therapeutically useful be subnormal in diabetics. Indeed, in a recent study, liver in diabetes. biopsies were performed on morbidly obese diabetics, morbidly obese subjects with normal glucose tolerance, HIGH-DOSE BIOTIN ENHANCES GLUCOKINASE and lean controls, all of whom were undergoing elec- SYNTHESIS tive abdominal surgery; hepatocyte glucokinase activity was found to be about 50% lower in the diabetics Studies dating back to the 1960s demonstrate that biotin than the other two groups (31). In rodents, hepatic GK status modulates GK activity in hepatocytes. Thus, liver is diminished by streptozotocin treatment, starvation, and GK activity was low in biotin-deficient rats (42), whereas high-fat feeding (10,32–24); the latter circumstance may pharmacological doses of biotin elevated this activity be considered a model for type II diabetes. in either biotin-deficient or normally fed rats (43-47). The It is not yet known whether β-cell GK activity is impact of administered biotin was most dramatic in rats

whose baseline GK activity was low owing to starvation, case in point is pyruvate kinase), this clearly is not the diabetes, or biotin-deficiency, but an increase of 40–50% case with PEPCK, as the effects of both insulin and biotin could be achieved even in healthy, normally fed rats. on its transcription can be observed within a few minutes. The effect of biotin was mediated by increased synthesis One likely possibility is that cGMP mediates the impact of GK (43–47); biotin clearly is not an essential cofactor of biotin on PEPCK; however, there appears to be little for GK, nor does it activate GK allosterically (42). if any published research regarding cGMP’s effect on Why biotin should modulate GK synthesis was initially PEPCK transcription. unclear. A breakthrough was achieved with the revela- tion that, in slightly supraphysiological concentrations BIOTIN FOR TREATMENT OF DIABETES (0.1–1 µM), biotin activates soluble guanylate cyclase by up to three-fold (48). This finding dovetailed nicely with These findings imply that supranutritional doses of biotin previous studies indicating that cGMP up-regulates may have therapeutic utility in diabetes. In fact, several insulin-stimulated expression of GK in hepatocytes, at least investigators have already explored this potential. High- in part by stimulating translation of previously existing dose oral or parenteral biotin has been shown to improve mRNA (26,49). Spence and Koudelka then conducted a oral glucose tolerance in diabetic KK mice (58), streptozo- series of experiments whose results were completely con- tocin-diabetic Wistar rats (53) and in pre-diabetic Otsuka sistent with the proposition that an increase in hepato- Long-Evans Tokushima Fatty rats (59). In the first pub- cyte cGMP levels mediates biotin’s enhancement of GK lished clinical report, Coggeshall and colleagues showed activity (50). (It is still unclear, however, whether the de- that biotin (16 mg daily orally) lowered fasting plasma crease of GK in biotin deficiency reflects a failure of biotin glucose in type I diabetics in whom insulin injections to activate guanylate cyclase; conceivably, a deficiency had been temporarily discontinued (60). of carboxylase activity (51) might play some role in Clearly the most important clinical report to date is this regard – or perhaps physiological biotin levels do that of Maebashi and colleague (61). These investigators influence basal guanylate cylcase activity.) More recently, reported the results of several protocols in which biotin nuclear run-on assays have demonstrated that biotin was administered to poorly controlled type II diabetics administration rapidly enhances the transcription of the in a dose of 3 mg t.i.d. These subjects had previously GK gene in the hepatocytes of starved rats (46). shown poor responsiveness to glibenclamide, which was The regulation of GK expression in pancreatic islets discontinued for at least a month prior to biotin treat- has been less thoroughly researched, nor is it known ment. In a placebo-controlled study, the 18 subjects how cGMP influences this expression. Nonetheless, a randomized to receive biotin had an average baseline very recent study demonstrates that biotin treatment fasting glucose of 12.9 mM; this fell significantly to elevates GK activity in an islet cell line (52), and another 7.1 mM after one month of biotin treatment. A month recent report demonstrates that i.p. biotin increases after the biotin had been discontinued, fasting glucose pancreatic GK activity by over two-fold in streptozotocin- had returned to its original level. In contrast, fasting diabetic rats (53). glucose remained virtually constant during placebo administration. The fact that fasting insulin levels did not decline in the biotin-treated subjects – despite the sharp BIOTIN REPRESSES PHOSPHOENOLPYRUVATE decline in glucose levels – is suggestive of improved β-cell CARBOXYKINASE function. The authors also enrolled 20 patients in a Phosphoenolpyruvate carboxykinase (PEPCK) is consi- longer-term open protocol. The findings here were com- dered rate-limiting for gluconeogenesis; its synthesis parable to those of the controlled study – fasting blood in hepatocytes is suppressed by insulin and induced glucose fell substantially, whereas insulin levels showed by glucagon/cAMP, glucocorticoids, and T3 (54,55). In- no evident change. However, it is notable that the initial creased hepatic expression of PEPCK presumably contri- trend in serum insulin was a slight non-significant butes to fasting hyperglycemia in diabetics, whereas decrease; this suggests that the primary impact of biotin suppression of this activity should be therapeutically was on hepatic function (perhaps owing to the privileged beneficial (56). This underlines the importance of recent access of the liver to oral biotin), while the apparent evidence that biotin administration to streptozotocin- improvement in β-cell function was of secondary im- diabetic rats (1 mg/kg, i.p.) rapidly inhibits transcription portance. In a third study with five subjects, patients of the PEPCK gene and subsequently decreases PEPCK who previously had been unresponsive to glibenclamide activity – an effect precisely parallel to that of insulin achieved virtual normalization of their fasting glucose administration (57). Whereas many effects of insulin and when half of the previous dose of this drug was used biotin on hepatic enzyme induction or activation are in conjunction with biotin. During the long-term studies, secondary consequences of glucokinase induction (a patients also received an anti-microbial drug that was

intended to prevent the proliferation of intestinal flora CHROMIUM SHOULD COMPLEMENT BIOTIN’S that might degrade the biotin; this drug by itself did not EFFICACY influence glycemic control, and no data were presented to document that it actually improved the response As noted, there is little reason to believe that biotin to oral biotin. Unfortunately, these studies did not assess therapy will directly improve the peripheral insulin re- oral glucose tolerance or glycated hemoglobin. Never- sistance that is the hallmark of, and precursor to, type theless, their results are striking and of potentially II diabetes. It is therefore of great interest that trivalent great importance. Presumably, they have received little chromium, when administered orally in a dose of attention to date owing to their publication in a journal 500 mcg b.i.d. as chromium picolinate, has recently been that is difficult to obtain in the West and not cited on reported to enhance insulin sensitivity (as measured by MedLine. the minimal model method) in moderately obese non- More recently, Greek physicians examined the impact diabetics (67). This follows on the heels of a large double- of i.v. biotin (50 mg post-dialysis) on four hemodialysis blind clinical study with poorly controlled Chinese type patients with impaired glucose tolerance; biotin treat- II diabetics, in which the same dosage of chromium picol- ment was followed by normalization of glucose tolerance inate was associated with a 30% reduction in glycated in three of the patient (62). hemoglobin during four months of treatment; the base-

No side-effects were noted in either of the clinical line average HbA1C of 9.4 fell significantly to 6.6, whereas studies in which biotin (9–16 mg daily) was administered the small decline in the placebo-treated group was not orally, nor in the hemodialysis study. Indeed, biotin is significant (68). In light of the minimal model study, the considered extremely safe, with no side-effects or tox- fact that chromium’s physiological role is to support icities noted in previous clinical studies with oral biotin insulin sensitivity (69), and in vitro studies showing that intakes up to 200 mg daily (63). chromium can improve insulin response in myoblasts The data cited above are consistent with the propo- and adipocytes (70,71), it is reasonable to suspect that sition that high-dose oral biotin can quite significantly increased peripheral insulin sensitivity was primarily re- improve glycemic control in diabetes by increasing GK sponsible for the clinical benefit observed in the Chinese expression in hepatocytes and β cells, while decreasing study. Like biotin, oral trivalent chromium is excep- hepatic PEPCK activity. One would thus expect to see a tionally safe (72,73), and no side-effects have been noted reduction in fasting glucose (owing to decreased hepatic to date in clinical studies with chromium picolinate – glucose output), an improvement in oral glucose toler- which has been used by millions of American consumers ance (owing to increased hepatic uptake of oral carbo- since 1989. hydrate) and, in type II diabetics, some improvement It is therefore reasonable to predict that the joint in glucose-stimulated insulin secretion. Since skeletal administration of biotin and chromium picolinate, in muscle and adipocytes do not express GK or PEPCK, any doses that are supranutritional but safe and well- observed improvement in peripheral insulin sensitivity tolerated, will benefit virtually every aspect of the type would presumably be a secondary consequence of these II diabetic syndrome, perhaps constituting a definitive effects. therapy for many diabetics whose disease is not too Of related interest is an anecdotal report that high-dose severe, and enabling substantial dose reductions in dia- biotin administration was associated with marked im- betics who still require drugs. The prospect of a safe, in- provement of severe peripheral neuropathy in three expensive, drug-free therapy for this distressing disorder diabetics; response was noted within four to eight weeks is exciting indeed; appropriate clinical trials are clearly (64). Since nitric oxide deficiency is thought to play a needed, both to confirm the efficacy of each nutrient role in the etiology of neuropathy (65) (nitric oxide being individually, and to assess the utility of their joint the physiological activator of guanylate cyclase), this administration. raises the intriguing possibility that high-dose biotin With respect to type I diabetes, while there is anecdotal therapy might be capable of raising cGMP levels systemi- evidence that chromium picolinate may reduce insulin cally – thus replicating some of the benefits achievable requirements in some type I diabetic (74), it is not yet with nitro-vasodilators or with measures that improve clear whether this will be associated with an improved endothelial function. Vasodilatory, anti-atherogenic, anti- quality of glycemic control. However, both a pilot clinical thrombotic, anti-inflammatory, and osteoprotective effects study (60), and results in streptozotocin-diabetic rats (53), might be anticipated. The systemic effects of biotin may suggest that high-dose biotin will be clinically useful be of particular value to diabetics, since endothelial in type I diabetics. Hepatic insulin activity must neces- dysfunction associated with a reduction in effective sarily be subnormal in insulin-treated type I patients, nitric oxide activity may be crucial to the genesis of the since systemic administration of insulin in safe doses complications of diabetes (66). cannot replicate the high portal concentrations of insulin

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