Mueller W M, Stanhope K L, Gregoire F, Evans J L, Havel P J
Department of Nutrition, University of California, Davis 95616, USA.
Obes Res. 2000 Oct;8(7):530-9. doi: 10.1038/oby.2000.66.
We have reported that glucose utilization regulates leptin expression and secretion from isolated rat adipocytes. In this study, we employed two antidiabetic agents that act to increase glucose uptake by peripheral tissues, metformin and vanadium, as pharmacological tools to examine the effects of altering glucose utilization on leptin secretion in primary cultures of rat adipocytes.
Isolated adipocytes (100 microL of packed cells per well) were anchored in a defined matrix of basement membrane components (Matrigel) with media containing 5.5 mM glucose and incubated for 96 hours with metformin or vanadium. Leptin secretion, glucose utilization, and lactate production were assessed.
Metformin (0.5 and 1.0 mM) increased glucose uptake in the presence of 0.16 nM insulin by 37 +/- 10% (p < 0.005) and 62 +/- 8% (p < 0.0001) over insulin alone, respectively. Metformin from 0.5 to 5.0 mM increased lactate production by 105 +/- 43% (p < 0.025) to 202 +/- 52% (p < 0.0025) and at 1.0 and 5.0 mM increased the proportional rate of glucose conversion to lactate by 78 +/- 18% (p < 0.005) and 166 +/- 41% (p < 0.0025), respectively. At concentrations less than 0.5 mM, metformin did not affect leptin secretion, but at 0.5 mM, the only concentration that significantly increased glucose utilization without increasing glucose conversion to lactate, leptin secretion was modestly stimulated (by 20 +/- 9%; p < 0.05). Concentrations from 1.0 to 25 mM inhibited leptin secretion by 25 +/- 8% (p < 0.005) to 89 +/- 4% (p < 0.0001). Across metformin doses, leptin secretion was inversely related to the percentage of glucose taken up and released as lactate (r = -0.74; p < 0.0001). Vanadium (5 to 20 microM) increased glucose uptake from 20 +/- 7% (p < 0.01) to 34 +/- 13% (p < 0.02) and increased lactate production at 5 microM by 17 +/- 8% (p < 0.025) and 10 microM by 61 +/- 20% (p < 0.02) but did not alter the conversion of glucose to lactate. Vanadium (5 to 50 microM) inhibited leptin secretion by 33 +/- 6% (p < 0.0025) to 61 +/- 8% (p < 0.0001).
Both metformin and vanadium increase glucose uptake and inhibit leptin secretion from cultured adipocytes. The inhibition of leptin secretion by metformin is related to an increase in the metabolism of glucose to lactate. The inhibition by vanadium most likely involves direct effects on cellular phosphatases. We hypothesize that the effect of glucose utilization to stimulate leptin production involves the metabolism of glucose to a fate other than anaerobic lactate production, possibly oxidation or lipogenesis.
我们曾报道葡萄糖利用可调节分离的大鼠脂肪细胞中瘦素的表达与分泌。在本研究中，我们使用两种可增加外周组织葡萄糖摄取的抗糖尿病药物二甲双胍和钒，作为药理学工具来研究改变葡萄糖利用对大鼠脂肪细胞原代培养物中瘦素分泌的影响。
将分离的脂肪细胞（每孔100微升压实细胞）固定于含有5.5 mM葡萄糖的基底膜成分（基质胶）的特定基质中，并用二甲双胍或钒孵育96小时。评估瘦素分泌、葡萄糖利用和乳酸生成情况。
在存在0.16 nM胰岛素的情况下，二甲双胍（0.5 mM和1.0 mM）分别使葡萄糖摄取量比单独使用胰岛素时增加37±10%（p<0.005）和62±8%（p<0.0001）。0.5至5.0 mM的二甲双胍使乳酸生成量增加105±43%（p<0.025）至202±52%（p<0.0025），1.0 mM和5.0 mM时分别使葡萄糖转化为乳酸的比例增加78±18%（p<0.005）和166±41%（p<0.0025）。浓度低于0.5 mM时，二甲双胍不影响瘦素分泌，但在0.5 mM时，这是唯一显著增加葡萄糖利用而不增加葡萄糖转化为乳酸的浓度，瘦素分泌受到适度刺激（增加20±9%；p<0.05）。1.0至25 mM的浓度使瘦素分泌受到抑制，抑制率为25±8%（p<0.005）至89±4%（p<0.0001）。在二甲双胍各剂量下，瘦素分泌与摄取并以乳酸形式释放的葡萄糖百分比呈负相关（r=-0.74；p<0.0001）。钒（5至20 microM）使葡萄糖摄取量从20±7%（p<0.01）增加至34±13%（p<0.02），5 microM时使乳酸生成量增加17±8%（p<0.025），10 microM时增加61±20%（p<0.02），但未改变葡萄糖向乳酸的转化。钒（5至50 microM）使瘦素分泌受到抑制，抑制率为33±6%（p<0.0025）至61±8%（p<0.0001）。
二甲双胍和钒均可增加培养的脂肪细胞对葡萄糖的摄取并抑制瘦素分泌。二甲双胍对瘦素分泌的抑制与葡萄糖代谢为乳酸的增加有关。钒的抑制作用很可能涉及对细胞磷酸酶的直接作用。我们推测葡萄糖利用刺激瘦素产生的作用涉及葡萄糖代谢为无氧乳酸生成以外的其他途径，可能是氧化或脂肪生成。
